LIBRARY 

OF   THK 

UNIVERSITY  OF  CALIFORN: 


Received 
Accession  No  . 


^^f-          >  ^ 
Class^  No  . 


SCIENCE     PRIMERS,  edited  by 

Professors   HUXLEY,   ROSCOE,  and 
BALFOUR  STEWART. 


IN  TROD  UCTOR  Y. 


>t«it«  llnmrrs. 


INTRODUCTORY. 


PROFESSOR   HUXLEY,   F.R.S. 


NEW  YORK  •:.  CINCINNATI  •:•  CHICAGO: 
AMERICAN     BOOK     COMPANY. 


SCIENCE   PRIMERS. 


EDITED  BY 
PROFESSORS   HUXLEY,    ROSCOE,    AND   BALFOUR   STEWART. 


r 

INTRODUCTORY T.  H.  HUXLEY 

CHEMISTRY H.  E.  ROSCOE 

PHYSICS BALFOUR  STEWART 

PHYSICAL  GEOGRAPHY A.  GEIKIE 

GEOLOGY A.  GEIKIE 

PHYSIOLOGY  AND 

HYGIENE  .....    M.  FOSTER  AND  R.  S.  TRACY 

ASTRONOMY J.  N.  LOCKYER 

BOTANY J.  D.  HOOKER 

LOGIC W.  S.  JEVONS 

INVENTIONAL  GEOMETRY .    .     .     .     W.  G.  SPENCER 

PIANOFORTE FRANKLIN  TAYLOR 

POLITICAL  ECONOMY W.  S.  JEVONS 

NATURAL  RESOURCES  OF  THE 

UNITED  STATES J.  H.  PATTON 


printed  b\> 

2D.  Bpplcton  &  Company 
mc\v  ii)orfc,  m.  S.  H. 


TABLE   OF   CONTENTS. 

ART.       SECT. 

I.  NATURE  AND  SCIENCE. 

PACK 

T.  ,,  Sensations  and  Things    ........       5 

2.  ,,  Causes  and  Effects 5 

3.  ,,  The  reason  Why.     Explanation     .        .        .        .        .        .6 

4.  ,,  Propert.es  and  Powers    .  7 

5.  „  Artificial  and  Natural  Objects.     Nature         ....       8 

6.  ,,  Artificial    Things    are    only    Natural    Things  shaped  and 

brought  together  or  separated  by  Men        .  .       8 

7.  ,,     Many  Objects  and  Chains  of  Causes  and  Effects  in  Nature 

are  out  of  our  reach     .         .  ...  10 

,,     The  Order  of  Nature :  nothing  happens  by  Accident,  and 

there  is  no  such  thing  as  Chance  .  10 

9.  ,,     Laws  of  Nature  ;   Laws,  are  not  Causes 12 

10.  ,,     Knowledge  of  Nature  is  the  Guide  of  Practical  Conduct  14 

11.  ,,     Science:  the  Knowledge  of  the  Laws  of  Nature  obtained  by 

Observation,  Experiment,  and  Reasoning  .        .        .16 

II.        MATERIAL  OBJECTS.— (A.)  MINERAL  BODIES. 

12.  ,,     The  Natural  Object  Water 19 

ij.  ,,     A  Tumbler  of  Water        .....  .        .     20 

14.  ,,     Water  occupies  Space  ;  it  offers  Resistance  .   it  has  Weight  ; 

and  is  able  to  transfer  Motion  which  it  has  acquired ;  it  is 
therefore  a  form  of  Matter 20 

15.  ,,     Water  is  a  liquid 21 

16.  ,,     Water  is  almost  incompressible       ......     22 

17.  ,,     The  Meaning  of  Weight 24 

18.  ,,     Gravity  and  Gravitation 25 

19.  ,,     The  cause  of  Weight :  Attraction:   Force      .        .        .        .27 

20.  , ,     The  Weight  of  Water  is  Proportioned  to  its  Bulk .        .        .28 

21.  .,     The  Measuring  of  Weights.     The  Balance    .         ...     29 

22.  .,     The  Weight  of  the  same  Bulk  or  Volume  of  Water  is  Con- 

stant under  the  same  conditions.     Mass.     Density    .         .     ;o 

23.  ,,     Equal  Volumes  of  Different  Things  under  the  same  circum- 

stances, have  Different  Weights  :  the  Density  of  Different 
Bodies  is  Different  .  ......  32 

24.  ,,     The  Meaning  of  Heavy  and  Light — Specific  Gravity    .        .     33 

25.  ,,     Things    of    greater   Specific   Gravity   than   Water  sink    in 

Water  ;  Things  of  less  Specific  Gravity  float      .         .  34 

26.  ,,     A  Body  which   Floats  in   Water  always  occupies  as  much 

Space  beneath  the  level  of  the  Surface  of  the  Water  as  is 
equal  to  the  Volume  of  Water  which  weighs  as  much  as  that 
Body  ;  in  other  words,  it  displaces  its  own  Weight  of  Water  36 

27.  ,,     Water  Presses  in  all  Directions 37 

23.  ,,     The  Transference  of  Motion  by  Moving  Water :  the  Momen- 

tum af  Moving  Water          .......     40 

29.  .,     The  Energy  of  Moving  Water 43 

30.  ,,     The  Properties  of  Water  are  Constant 47 

31-  »     Increase  of  Heatat first  causes  Water  to  Increase  in  Volume     48 

32.  ,,     Increase  of  Heat  at  length  causes  Water  to  becc  me  Steam    .     50 

33.  „     The  taking  away  of  Heat  from  Steam  causes  the  Steam  to 

change  into  Hot  Water        .......     51 

34.  „     When   Water  is  changed  into  Steam,  its  Volume  becomes 

about  1,700  times  greater  than  it  was  at  first      .        .  51 

35-  »     Gases  or  Elastic  Fluids.     Air ;  .  52 

S'j.  ,,     Steam  is  an  Elastic  Fluid  or  Gas •  •  54 

37.  ,,     Gases  and  Vapours 55 

38.  „     The  Evaporation  of  Water  at  ordinary  Temperatures   .         .  56 
39-           «»     When  Hot  Water  is  cooled,  it  Contracts  to  beg  n  with,  but 

after  a  time  Expands .57 


TABLE   OF  CONTENTS. 


ART.      SECT.  PAGE 

40.  II.     Water  cooled  still  further  becomes  the  transparent  brittle 

solid  Ice .         .58 

41.  „     Ice  has  less  Specific  Gravity  than  the  Water  from  which  it 

was  formed  .........     59 

42.  ,,    Hoar  Frost  is  the  Gaseous  Water  which  exists  in  the  Atmos- 

phere, condensed  and  converted  into  Ice  Crystals      .         .     60 

43.  ,,    When  Ice  is  warmed  it  begins  to  change  back  into  Water  as 

soon  as  the  Temperature  reaches  3  ^0  »         .         .         .         .     61 

44.  ,,     Ice  the  solid,  Water  the  liquid,  and  Steam  the  gas,  are  three 

states  of  one  natural  object ;  the  condition  of  each  state 
being  a  certain  amount  of  Heat £2 

45.  „     The  Phenomena  of  Heat  are  the  Effects  of  a  rapid  Motion  of 

the  Particles  of  M  atter 63 

46.  ,,    The  Structure  of  Water (5 

47.  .,     Suppositions  or  Hypotheses  ;  their  Uses  and  their  Value      .  £7 

48.  ,,     The  Hypothesis  that  Water  is  composed  of  Separate  Parti- 

cles (Molecules)  CB 

49.  ,,     All  Matter  is  probably  made  up  either  of  Molecules  or  of 

Atoms  ...........  70 

50  ,,     Elementary  Bodies  are  neither  destroyed  nor  is  their  Quantity 

increased  in  Nature 72 

51.  ,,     Simple  Mixture .  73 

52.  „     Mixture  followed  by  Increase  of  Density;  Alcohol  and  Water  74 

53.  ,,     Solution:  Water  Dissolves  Salt      .         .         .         .         .         .76 

54.  ,,     Quicklime  and  Water :  Plaster  of  Paris  and  Water :  Com- 

bination       ..........     79 

55.  „     Mineral  bodies  may  take  on  definite  shapes  and  grow,  c  r 

increase  in  size,  by  the  addition  of  like  parts      .        .        .82 

(B.)  LIVING  BODIES. 

56.  ,,     The  Wheat  Plant  and  the  substances  of  which  it  is  composed    83 

57.  ,,     The  common  Fowl  and  the  Substances  of  which  it  is  com- 

posed      85 

58.  ,,     Certain  Constituents  of  the  Body  are  very  similar  in  the 

Wheat  Plant  and  in  the  Fowl      .  .86 

5;.  ,,     Proteid  Substances  are  met  with  in  Nature  only  in  Animals 

and  Plants ;  and  Animals  and  Plants  always  contain  Pro- 

teids 87 

Co  ,,     What  is  meant  by  the  word  Living  ? 88 

Ci.  „    The  Living  Plant  increases  in  Size,  by  adding  to  the  Sub- 

stances which  compose  its  Body,  like  Substances  ;  these, 
however,  are  not  derived  from  without,  but  are  manufac- 
tured within  the  Body  of  the  Plant  from  simpler  Materials  88 

62.  ,,     The  Living  Plant,  after  it  has  grown  up,  detaches  part  of  ks 

Substance,  which  has  the  Power  of  developing  into  a 
similar  Plant,  as  a  Seed 90 

63.  _        ,,     The  Living  Animal  increases  in  Size  by  adding  to  the  Sub- 

stances which  compose  its  Body,  like  Substances  ;  these 
however  are  chiefly  derived  directly  from  other  Animals 
or  from  Plants .90 

64.  ,,     The  Living  Animal,  after  it  has  grown  up,  detaches  part  of 

its  Substance,  which  has  the  Power  of  growing  into  a 

similar  Animal,  as  an  Egg 91 

65  ,,     Living  Bodies  differ  from  Mineral  Bodies  in  their  Essential 

Composition,  in  the  manner  of  their  Growth,  and  in  the 
fact  that  they  are  reproduced  by  Germs  .  .  .  .91 

III.  IMMATERIAL  OBJECTS. 

66.  ,,     Mental  Phenomena 92 

67.  ,,    The  order  of  Mental  Phenomena :  Psychology      .        .        .93 


SCIENCE    PRIMERS. 


INTRODUCTORY. 


I.  NATURE  AND  SCIENCE. 

i.  Sensations  and  Things. 

All  the  time  that  we  are  awake  we  are  learning  by 
means  of  our  senses  something  about  the  world  in 
which  we  live  and  of  which  we  form  a  part ;  we  are 
constantly  aware  of  feeling,  or  hearing,  or  smelling, 
and,  unless  we  happen  to  be  in  the  dark,  of  seeing  ;  at 
intervals  we  taste.  We  call  the  information  thus 
obtained  sensation. 

When  we  have  any  of  these  sensations  we  com- 
monly say  that  we  feel,  or  hear,  or  smell,  or  see,  or 
taste,  something.  A  certain  scent  makes  us  say 
we  smell  onions ;  a  certain  flavour,  that  we  taste 
apples ;  a  certain  sound,  that  we  hear  a  carnage ;  a 
certain  appearance  before  our  eyes,  that  we  see  a 
tree  ;  and  we  call  that  which  we  thus  perceive  by  the 
aid  of  our  senses  a  thing  or  an  object. 

2.  Causes  and  Effects. 

Moreover,  we  say  of  all  these  things,  or  objects,  that 
they  are  the  causes  of  the  sensations  in  question,  and 


6  SCIENCE  PRIMERS.          [NATURE  AX n 

that  the  sensations  are  the  effects  of  these  causes. 
For  example,  if  we  hear  a  certain  sound,  we  say  it  is 
caused  by  a  carriage  going  along  the  road,  or  that  it  is 
the  effect,  or  the  consequence,  of  a  carriage  passing 
along.  If  there  is  a  strong  smell  of  burning,  we  believe 
it  to  be  the  effect  of  something  on  fire,  and  look  about 
anxiously  for  the  cause  of  the  smell.  If  we  see  a  tree, 
we  believe  that  there  is  a  thing,  or  object,  which  is  the 
cause  of  that  appearance  in  our  field  of  view. 

3.  The  reason  Why.     Explanation. 

In  the  case  of  the  smell  of  burning,  when  we  find 
on  looking  about,  that  something  actually  is  on  fire, 
we  say  indifferently  either  that  we  have  found  out  the 
cause  of  the  smell,  or  that  we  know  the  reason  why 
we  perceive  that  smell ;  or  that  we  have  explained 
it.  So  that  to  know  the  reason  why  of  anything,  or  to 
explain  it,  is  to  know  the  cause  of  it.  But  that  which 
is  the  cause  of  one  thing  is  the  effect  of  another. 
Thus,  suppose  we  find  some  smouldering  straw  to  be 
the  cause  of  the  smell  of  burning,  we  immediately  ask 
what  set  it  on  fire,  or  what  is  the  cause  of  its  burning  ? 
Perhaps  we  find  that  a  lighted  lucifer  match  has  been 
thrown  into  the  straw,  and  then  we  say  that  the  lighted 
match  was  the  cause  of  the  fire.  But  a  lucifer  match 
would  not  be  in  that  place  unless  some  person  had 
put  it  there.  That  is  to  say,  the  presence  of  the 
lucifer  match  is  an  effect  produced  by  somebody  as 
cause.  So  we  ask  why  did  any  one  put  the  match 
there  ?  Was  it  done  carelessly,  or  did  the  person  who 
put  it  there  intend  to  do  so  ?  And  if  so,  what  was 
his  motive,  or  the  cause  which  led  him  to  do  such  a 
thing  ?  And  what  was  the  reason  for  his  having  such 


SCIENCE.]  INTRODUCTORY.  7 

a  motive  ?  It  is  plain  that  there  is  no  end  to  the 
questions,  one  arising  out  of  the  other,  that  might  be 
asked  in  this  fashion. 

Thus  we  believe  that  everything  is  the  effect  of 
something  which  preceded  it  as  its  cause,  and  that 
this  cause  is  the  effect  of  something  else,  and  so  on, 
through  a  chain  of  causes  and  effects  which  goes  back 
as  far  as  we  choose  to  follow  it.  Anything  is  said  to 
be  explained  as  soon  as  we  have  discovered  its  cause, 
or  the  reason  why  it  exists  ;  the  explanation  is  fuller, 
if  we  can  find  out  the  cause  of  that  cause  ;  and  the 
further  we  can  trace  the  chain  of  causes  and  effects, 
the  more  satisfactory  is  the  explanation.  But  no 
explanation  of  anything  can  be  complete,  because 
human  knowledge,  at  its  best,  goes  but  a  very  little 
way  back  towards  the  beginning  of  things. 

4.  Properties  and  Powers. 

When  a  thing  is  found  always  to  cause  a  particular 
effect,  we  call  that  effect  sometimes  a  property, 
sometimes  a  power  of  the  thing.  Thus  the  odour 
of  onions  is  said  to  be  a  property  of  onions,  because 
onions  always  cause  that  particular  sensation  of 
smell  to  arise,  when  they  are  brought  near  the 
nose ;  lead  is  said  to  have  the  property  of  heaviness, 
because  it  always  causes  us  to  have  the  feeling  of 
weight  when  we  handle  it ;  a  stream  is  said  to  have 
the  power  to  turn  a  waterwheel,  because  it  causes  the 
waterwheel  to  turn  ;  and  a  venomous  snake  is  said  to 
have  the  power  to  kill  a  man,  because  its  bite  may 
cause  a  man  to  die.  Properties  and  powers,  then,  are 
certain  effects  caused  by  the  things  which  are  said  to 
possess  them. 


8  SCIENCE  PRIMERS.         [NATURE  AND 

5.  Artificial  and  Natural  Objects.    Nature. 

A  great  many  of  the  things  brought  to  our 
knowledge  by  our  senses,  such  as  houses  and  furniture, 
carnages  and  machines,  are  termed  artificial  things 
or  objects,  because  they  have  been  shaped  by  the 
art  of  man ;  indeed,  they  are  generally  said  to  be 
made  by  man.  But  a  far  greater  number  of  things 
owe  nothing  to  the  hand  of  man,  and  would  be  just 
what  they  are  if  mankind  did  not  exist, — such  as  the 
sky  and  the  clouds ;  the  sun,  moon  and  stars ;  the  sea 
with  its  rocks  and  shingly  or  sandy  shores ;  the  hills 
and  dales  of  the  land ;  and  all  wild  plants  and  animals. 
Things  of  this  kind  are  termed  natural  objects,  and 
to  the  whole  of  them  we  give  the  name  of  Nature. 

6.  Artificial  Things  are  only  Natural  Things 
shaped  and  brought  together  or  separated  by 
Men. 

Although  this  distinction  between  nature  and  art, 
between  natural  and  artificial  things,  is  very  easily 
made  and  very  convenient,  it  is  needful  to  remember 
that,  in  the  long  run,  we  owe  everything  to  nature ; 
that  even  those  artificial  objects  which  we  commonly 
say  are  made  by  men,  are  only  natural  objects  shaped 
and  moved  by  men;  and  that,  in  the  sense  of  creating, 
that  is  to  say,  of  causing  something  to  exist  which 
did  not  exist  in  some  other  shape  before,  man  can 
make  nothing  whatever.  Moreover,  we  must  recollect 
that  what  men  do  in  the  way  of  shaping  and  bringing 
together  or  separating  natural  objects,  is  done  in  virtue 
of  the  powers  which  they  themselves  possess  as  natural 
objects. 


SCIENCE.]  INTRODUCTORY.  9 

Artificial  things  are,  in  fact,  all  produced  by  the 
action  of  that  part  of  nature  which  we  call  mankind, 
upon  the  rest. 

We  talk  of  "making  "  a  box,  and  rightly  enough,  if 
we  mean  only  that  we  have  shaped  the  pieces  of  wood 
and  nailed  them  together ;  but  the  wood  is  a  natural 
object  and  so  is  the  iron  of  the  nails.  A  watch  is 
"  made  "  of  the  natural  objects  gold  and  other  metals, 
sand,  soda,  rubies,  brought  together,  and  shaped  in 
various  ways  ;  a  coat  is  "  made ;;  of  the  natural  object, 
wool ;  and  a  frock  of  the  natural  objects,  cotton  or 
silk.  Moreover,  the  men  who  make  all  these  things 
are  natural  objects. 

Carpenters,  builders,  shoemakers,  and  all  other 
artisans  and  artists,  are  persons  who  have  learned  so 
much  of  the  powers  and  properties  of  certain  natural 
objects,  and  of  the  chain  of  causes  and  effects  in 
nature,  as  enables  them  to  shape  and  put  together  those 
natural  objects,  so  as  to  make  them  useful  to  man. 

A  carpenter  could  not,  as  we  say,  "  make  "  a  chair 
unless  he  knew  something  of  the  properties  and 
powers  of  wood ;  a  blacksmith  could  not  "  make  "  a 
horseshoe  unless  he  knew  that  it  is  a  property  of  iron 
to  become  soft  and  easily  hammered  into  shape  when 
it  is  made  red-hot ;  a  brickmaker  must  know  many  of 
the  properties  of  clay ;  and  a  plumber  could  not  do 
his  work  unless  he  knew  that  lead  has  the  properties 
of  softness  and  flexibility,  and  that  a  moderate  heat 
causes  it  to  melt. 

So  that  the  practice  of  every  art  implies  a  certain 
knowledge  of  natural  causes  and  effects;  and  the 
improvement  of  the  arts  depends  upon  our  learning 
more  and  more  of  the  properties  and  powers  of  natural 


•- 
f^-  OF 


io  SCIENCE  PRIMERS.         [NATURE  AND 

objects,  and  discovering  how  to  turn  the  properties 
and  the  powers  of  things  and  the  connections  of  cause 
and  effect  among  them  to  our  own  advantage. 

7.  Many  Objects  and  Chains  of  Causes  and 
Effects  in  Nature  are  out  of  our  reach. 

Among  natural  objects,  as  we  have  seen,  there 
are  some  that  we  can  get  hold  of  and  turn  to 
account.  But  all  the  greatest  things  in  nature  and  the 
links  of  cause  and  effect  which  connect  them,  are 
utterly  beyond  our  reach.  The  sun  rises  and  sets ; 
the  moon  and  the  stars  move  through  the  sky ;  fine 
weather  and  storms,  cold  and  heat,  alternate.  The 
sea  changes  from  violent  disturbance  to  glassy  calm, 
as  the  winds  sweep  over  it  with  varying  strength  or 
die  away;  innumerable  plants  and  animals  come  in 
being  and  vanish  again,  without  our  being  able  to  exert 
the  slightest  influence  on  the  majestic  procession  of  the 
series  of  great  natural  events.  Hurricanes  ravage  one 
spot ;  earthquakes  destroy  another ;  volcanic  eruptions 
lay  waste  a  third.  A  fine  season  scatters  wealth  and 
abundance  here,  and  a  long  drought  brings  pestilence 
and  famine  there.  In  all  such  cases,  the  direct 
influence  of  man  avails  him  nothing ;  and,  so  long 
as  he  is  ignorant,  he  is  the  mere  sport  of  the  greater 
powers  of  nature. 

8.  The  Order  of  Nature  :  nothing  happens 
by  Accident,  and  there  is  no  such  thing  as 
Chance. 

But  the  first  thing  that  men  learned,  as  soon  as 
they  began  to  study  nature  carefully,  was  that  some 
events  take  place  in  regular  order  and  that  some  causes 


SCIENCE.]  INTRODUCTORY.  " 

always  give  rise  to  the  same  effects.  The  sun  always 
rises  on  one  side  and  sets  on  the  other  side  of  the 
sky ;  the  changes  of  the  moon  follow  one  another  in 
the  same  order  and  with  similar  intervals  ;  some  stars 
never  sink  below  the  horizon  of  the  place  in  which 
we  live  ;  the  seasons  are  more  or  less  regular ;  water 
always  flows  down-hill ;  fire  always  burns ;  plants 
grow  up  from  seed  and  yield  seed,  from  which  like 
plants  grow  up  again ;  animals  are  born,  grow,  reach 
maturity,  and  die,  age  after  age,  in  the  same  way. 
Thus  the  notion  of  an  order  of  nature  and  of  a 
fixity  in  the  relation  of  cause  and  effect  between 
things  gradually  entered  the  minds  of  men.  So  far 
as  such  order  prevailed  it  was  felt  that  things  were 
explained  /  while  the  things  that  could  not  be  ex- 
plained were  said  to  have  come  about  by  chance,  or 
to  happen  by  accident. 

But  the  more  carefully  nature  has  been  studied,  the 
more  widely  has  order  been  found  to  prevail,  while 
what  seemed  disorder  has  proved  to  be  nothing  but 
complexity;  until,  at  present,  no  one  is  so  foolish  as 
to  believe  that  anything  happens  by  chance,  or  that 
there  are  any  real  accidents,  in  the  sense  of  events 
which  have  no  cause.  And  if  we  say  that  a  thing 
happens  by  chance,  everybody  admits  that  all  we 
really  mean  is,  that  we  do  not  know  its  cause  or 
the  reason  why  that  particular  thing  happens.  Chance 
and  accident  are  only  aliases  tf.  ignorance. 

At  this  present  moment,  as  I  look  out  of  my  window, 
it  is  raining  and  blowing  hard,  and  the  branches  of  the 
trees  are  waving  wildly  to  and  fro.  It  may  be  that  a 
man  has  taken  shelter  under  one  of  these  trees ;  perhaps, 
if  a  stronger  gust  than  usual  comes,  a  brarch  will  break, 
2 


12  SCIENCE  PRIMERS.          [NATURE  AND 

fall  upon  the  man,  and  seriously  hurt  him.  If  that 
happens  it  will  be  called  an  "accident,"  and  the  man 
will  perhaps  say  that  by  "  chance  "  he  went  out,  and 
then  "  chanced  "  to  take  refuge  undor  the  tree,  and  so 
the  "  accident "  happened.  But  there  is  neither  chance 
nor  accident  in  the  matter.  The  storm  is  the  effect  of 
causes  operating  upon  the  atmosphere,  perhaps  hun- 
dreds of  miles  away  ;  every  vibration  of  a  leaf  is  the 
consequence  of  the  mechanical  force  of  the  wind 
acting  on  the  surface  exposed  to  it ;  if  the  bough 
breaks,  it  will  do  so  in  consequence  of  the  relation 
between  its  strength  and  the  force  of  the  wind  ;  if  it 
falls  upon  the  man  it  will  do  so  in  consequence- of  the 
action  of  other  definite  natural  causes  ;  and  the  posi- 
tion of  the  man  under  it  is  only  the  last*  term  in  a 
series  of  causes  and  effects,  which  have  followed  one 
another  in  natural  order,  from  that  cause,  the  effect  of 
which  was  his  setting  out,  to  that  the  effect  of  which 
was  his  stepping  under  the  tree. 

But,  inasmuch  as  we  are  not  wise  enough  to  be  able 
to  unravel  all  these  long  and  complicated  series  of 
causes  and  effects  which  lead  to  the  falling  of  the 
branch  upon  the  man,  we  call  such  an  event  an 
accident. 

9.  Laws  of  Nature  ;  Laws  are  not  Causes. 

When  we  have  made  out  by  careful  and  repeated 
observation  that  something  is  always  the  cause  of  a 
certain  effect,  or  that  certain  events  always  take  place 
in  the  same  order,  we  speak  of  the  truth  thus  dis- 
covered as  a  law  of  nature.  Thus  it  is  a  law  of 
nature  that  anything  heavy  falls  to  the  ground  if  it  is 


SCIENCE.]  INTRODUCTORY.  13 


unsupported  ;  it  is  a  law  of  nature  that,  under  or- 
dinary conditions,  lead  is  soft  and  heavy,  while  flint 
is  hard  and  brittle  ;  because  experience  shows  us  that 
heavy  things  always  do  fall  if  they  are  unsupported, 
that,  under  ordinary  conditions,  lead  is  always  soft 
and  that  flint  is  always  hard. 

In  fact,  everything  that  we  know  about  the  powers 
and  properties  of  natural  objects  and  about  the  order 
of  nature  may  properly  be  termed  a  law  of  nature. 
But  it  is  desirable  to  remember  that  which  is  very 
often  forgotten,  that  the  laws  of  nature  are  not  the 
causes  of  the  order  of  nature,  but  only  our  way  of 
stating  as  much  as  we  have  .made  out  of  that  order. 
Stones  do  not  -fall  to  the  ground  in  consequence  of 
the  law  just  stated,  as  people  sometimes  carelessly 
say  •  but  the  law  is  a  way  of  asserting  that  which  in- 
variably happens  when  heavy  bodies  at  the  surface  of 
the  earth,  stones  among  the  rest,  are  free  to  move. 

The  laws  of  nature  are,  in  fact,  in  this  respect,  similar 
to  the  laws  which  men  make  for  the  guidance  of  their 
conduct  towards  one  another.  There  are  laws  about 
the  payment  of  taxes,  and  there  are  laws  against 
stealing  or  murder.  But  the  law  is  not  the  cause  of  a 
man's  paying  his  taxes,  nor  is  it  the  cause  of  his 
abstaining  from  theft  and  murder.  The  law  is  simply 
a  statement  of  what  will  happen  to  a  man  if  he  does 
not  pay  his  taxes,  and  if  he  commits  theft  or  murder; 
and  the  cause  of  his  paying  his  taxes,  or  abstaining 
from  crime  (in  the  absence  of  any  better  motive)  is  the 
fear  of  consequences  which  is  the  effect  of  his  belief 
in  that  statement.  A  law  of  man  tells  what  we  may 
expect  society  will  do' under  certain  circumstance ; 
and  a  law  of  nature  tells  us  what  we  may  expect 


i4  SCIENCE  PRIMERS.         [NATURE  AND 

natural  objects  will  do  under  certain  circumstances. 
Each  contains  information  addressed  to  our  intelligence, 
and  except  so  far  as  it  influences  our  intelligence,  it  is 
merely  so  much  sound  or  writing. 

While  there  is  this  much  analogy  between  human 
and  natural  laws,  however,  certain  essential  differences 
between  the  two  must  not  be  overlooked.  Human 
law  consists  of  commands  addressed  to  voluntary 
agents,  which  they  may  obey  or  disobey ;  and  the 
law  is  not  rendered  null  and  void  by  being  broken. 
Natural  laws,  on  the  other  hand,  are  not  commands 
but  assertions  respecting  the  invariable  order  of 
nature ;  and  they  remain  laws  only  so  long  as  they 
can  be  shown  to  express  that  order.  To  speak  of  the 
violation,  or  the  suspension,  of  a  law  of  nature  is  an 
absurdity.  All  that  the  phrase  can  really  mean  is 
that,  under  certain  circumstances  the  assertion  con- 
tained in  the  law  is  not  true  ;  and  the  just  conclusion 
is,  not  that  tha  order  of  nature  is  interrupted,  but 
that  we  have  made  a  mistake  in  stating  that  order. 
A  true  natural  law  is  an  universal  rule,  and,  as  such, 
admits  of  no  exceptions. 

Again,  human  laws  have  no  meaning  apart  from  the 
existence  of  human  society.  Natural  laws  express  the 
general  course  of  nature,  of  which  human  society 
forms  only  an  insignificant  fraction. 

10.  Knowledge  of  Nature  is  the  Guide  of 
Practical  Conduct. 

If  nothing  happens  by  chance,  but  everything  in 
nature  follows  a  definite  order,  and  if  the  laws  of 
nature  embody  that  which  we  have  been  able  to  learn 


SCIENCE.]  INTRODUCTORY.  15 

about  the  order  of  nature  in  accurate  language,  then 
it  becomes  very  important  for  us  to  know  as  many  as 
we  can  of  these  laws  of  nature,  in  order  that  we  may 
guide  our  conduct  by  them. 

Any  man  who  should  attempt  to  live  in  a  country 
without  reference  to  the  laws  of  that  country  would 
very  soon  find  himself  in  trouble ;  and  if  he  were 
fined,  imprisoned,  or  even  hanged,  sensible  people 
would  probably  consider  that  he  had  earned  his  fate 
by  his  folly. 

In  like  manner,  any  one  who  tries  to  live  upon  the 
face  of  this  earth  without  attention  to  the  laws  of 
nature  will  live  there  for  but  a  very  short  time,  most 
of  which  will  be  passed  in  exceeding  discomfort ;  a 
peculiarity  of  natural  laws,  as  distinguished  from  those 
of  human  enactment,  being  that  they  take  effect 
without  summons  or  prosecution.  In  fact,  nobody 
could  live  for  half  a  day  unless  he  attended  to  some 
of  the  laws  of  nature ;  and  thousands  of  us  are  dying 
daily,  or  living  miserably,  because  men  have  not  yet 
been  sufficiently  zealous  to  learn  the  code  of  nature. 

It  has  already  been  seen  that  the  practice  of  all 
our  arts  and  industries  depends  upon  our  knowing 
the  properties  of  natural  objects  which  we  can  get 
hold  of  and  put  together ;  and  though  we  may  be 
able  to  exert  no  direct  control  over  the  greater 
natural  objects  and  the  general  succession  of  causes 
and  effects  in  nature,  yet,  if  we  know  the  properties 
and  powers  of  these  objects,  and  the  customary  order 
of  events,  we  may  elude  that  which  is  injurious  to  us, 
and  profit  by  that  which  is  favourable. 

Thus,  though  men  can  nowise  alter  the  seasons  or 
change  the  process  of  growth  in  plants,  yet  having 


16  SCIENCE  PRIMERS.         [NATURE  AND 

learned  the  order  of  nature  in  these  matters,  they 
make  arrangements  for  sowing  and  reaping  accord- 
ingly ;  they  cannot  make  the  wind  blow,  but  when  it 
does  blow  they  take  advantage  of  its  known  powers 
and  probable  direction  to  sail  ships  and  turn  wind- 
mills ;  they  cannot  arrest  the  lightning,  but  they  can 
make  it  harmless  by  means  of  conductors,  the  con- 
struction of  which  implies  a  knowledge  of  some  of  the 
laws  of  that  electricity,  of  which  lightning  is  one  of 
the  manifestations.  Forewarned  is  forearmed,  says 
the  proverb ;  and  knowledge  of  the  laws  of  nature  is 
forewarning  of  that  which  we  may  expect  to  happen, 
when  we  have  to  deal  with  natural  objects. 

ii.  Science:  the  Knowledge  of  the  Laws 
of  Nature  obtained  by  Observation,  Experi- 
ment, and  Reasoning. 

No  line  can  be  drawn  between  common  knowledge 
of  things  and  scientific  knowledge ;  nor  between  com- 
mon reasoning  and  scientific  reasoning.  In  strictness 
all  accurate  knowledge  is  Science  ;  and  all  exact 
reasoning  is  scientific  reasoning.  The  method  of 
observation  and  experiment  by  which  such  great 
results  are  obtained  in  science,  is  identically  the  same 
as  that  which  is  employed  by  every  one,  every  day  of 
his  life,  but  refined  and  rendered  precise.  If  a  child 
acquires  a  new  toy,  he  observes  its  characters  and  ex- 
periments upon  its  properties;  arid  we  are  all  of  us 
constantly  making  observations  and  experiments  upon 
one  thing  or  another. 

But  those  who  have  never  tried  to  observe  accu- 
rately will  be  surprised  to  find  how  difficult  a  business 
it  is.  There  is  not  one  person  in  a  hundred  who  can 


SCIENCE.]  INTRODUCTORY.  17 

describe  the  commonest  occurrence  with  even  an  ap- 
proach to  accuracy.  That  is  to  say,  either  he  will 
omit  something  which  did  occur,  and  which  is  of  im- 
portance ;  or  he  will  imply  or  suggest  the  occurrence 
of  something  which  he  did  not  actually  observe,  but 
which  he  unconsciously  infers  must  have  happened. 
When  two  truthful  witnesses  contradict  one  another 
in  a  court  of  justice,  it  usually  turns  out  that  one  or 
other,  or  sometimes  both,  are  confounding  their  in- 
ferences from  what  they  saw  with  that  which  they 
actually  saw.  A  swears  that  B  picked  his  pocket. 
It  turns  out  that  all  that  A  really  knows  is  that  he 
felt  a  hand  in  his  pocket  when  B  was  close  to  him ; 
and  that  B  was  not  the  thief,  but  C,  whom  A  did  not 
observe.  Untrained  observers  mix  up  together  their 
inferences  from  what  they  see  with  that  which  they 
actually  see  in  the  most  wonderful  way;  and  even 
experienced  and  careful  observers  are  in  constant 
danger  of  falling  into  the  same  error. 

Scientific  observation  is  such  as  is  at  once  full, 
precise,  and  free  from  unconscious  inference. 

Experiment  is  the  observation  of  that  which  hap- 
pens when  we  intentionally  bring  natural  objects 
together,  or  separate  them,  or  in  any  way  change 
the  conditions  under  which  they  are  placed.  Scien- 
tific experiment,  therefore,  is  scientific  observation  per- 
formed under  accurately  known  artificial  conditions. 

It  is  a  matter  of  common  observation  that  water 
sometimes  freezes.  The  observation  becomes  scien- 
tific when  we  ascertain  under  what  exact  conditions 
the  change  of  water  into  ice  takes  place.  The  com- 
monest experiments  tell  us  that  wood  floats  in  water. 


18  SCIENCE  PRIMERS.          [NATURE  AND 


Scientific  experiment  shew  s  that,  in  floating,  it  displaces 
its  own  weight  of  the  water. 

Scientific  reasoning  differs  from  ordinary  reason- 
ing in  just  the  same  way  as  scientific  observation  and 
experiment  differ  from  ordinary  observation  and  ex- 
periment— that  is  to  say,  it  strives  to  be  accurate  ; 
and  it  is  just  as  hard  to  reason  accurately  as  it  is  to 
observe  accurately. 

In  scientific  reasoning  general  rules  are  collected 
from  the  observation  of  many  particular  cases  ;  and, 
when  these  general  rules  are  established,  conclusions 
are  deduced  from  them,  just  as  in  every-day  life.  If 
a  boy  says  that  "  marbles  are  hard,"  he  has  drawn 
a  conclusion  as  to  marbles  in  general  from  the 
marbles  he  happens  to  have  seen  and  felt,  and  has 
reasoned  in  that  mode  which  is  technically  termed 
induction.  If  he  declines  to  try  to  break  a  marble 
with  his  teeth,  it  is  because  he  consciously,  or  un- 
consciously, performs  the  converse  operation  of  de- 
duction from  the  general  rule  "  marbles  are  too  hard 
to  break  with  one's  teeth." 

You  will  learn  more  about  the  process  of  reasoning 
when  you  study  Logic,  which  treats  of  that  subject  in 
full.  At  present,  it  is  sufficient  to  know  that  the  laws 
of  nature  are  the  general  rules  respecting  the  be- 
haviour of  natural  objects,  which  have  been  collected 
from  innumerable  observations  and  experiments  ;  or,  in 
other  words,  that  they  are  inductions  from  those 
observations  and  experiments.  The  practical  and 
theoretical  results  of  science  are  the  products 
of  deductive  reasoning  from  these  general  rules. 

Thus  science  and  common  sense  are  not  opposed, 
as  people  sometimes  fancy  them  to  be,  but  science  is 


SCIENCE.]  INTRODUCTORY.  19 

perfected  common  sense.  Scientific  reasoning  is 
simply  very  careful  common  reasoning,  and  common 
knowledge  grows  into  scientific  knowledge  as  it  be- 
comes more  and  more  exact  and  complete. 

The  way  to  science  then  lies  through  common  know- 
ledge ;  we  must  extend  that  knowledge  by  careful  ob- 
servation and  experiment,  and  learn  how  to  state  the 
results  of  our  investigations  accurately,  in  general 
rales  or  laws  of  nature ;  finally,  we  must  learn  how 
to  reason  accurately  from  these  rules,  and  thus  arrive 
at  rational  explanations  of  natural  phenomena,  which 
may  suffice  for  our  guidance  in  life. 


II.  MATERIAL  OBJECTS.— A.  MINERAL  BODIES. 

12.  The  Natural  Object  Water. 

One  of  the  commonest  of  common  natural  objects 
is  water ;  everybody  uses  it  in  one  way  or  another 
every  day ;  and  consequently  everybody  possesses  a 
store  of  loose  information — of  common  knowledge — 
about  it.  But,  in  all  probability,  a  great  deal  of  this 
knowledge  has  never  been  attended  to  by  its  pos- 
sessor ;  and  certainly,  those  who  have  never  tried  to 
learn  how  much  may  be  known  about  water,  will  be 
ignorant  of  a  great  many  of  its  powers  and  properties 
and  of  the  laws  of  nature  which  it  illustrates;  and 
consequently  will  be  unable  to  account  for  many 
things  of  which  the  explanation  is  very  easy.  So 
we  may  as  well  make  a  beginning  of  science  by 
studying  water. 


20  SCIENCE  PRIMERS.  [MATERIAL 

13.  A  Tumbler  of  Water. 

Suppose  we  have  a  tumbler  half- full  of  water.  The 
tumbler  is  an  artificial  object  (§5);  that  is  to  say, 
certain  natural  objects  have  been  brought  together 
and  heated  till  they  melted  into  glass,  and  this  glass 
has  been  shaped  by  a  workman.  The  water,  on  the 
other  hand,  is  a  natural  object,  which  has  come  from 
some  river,  pond,  or  spring;  or  it  may  be  from  a 
water-butt  into  which  the  rain  which  has  fallen  on 
the  roof  of  a  house  has  flowed. 

Now  the  water  has  a  vast  number  of  peculiarities. 
For  example,  it  is  transparent,  so  that  you  can  see 
through  it ;  it  feels  cool ;  it  will  quench  thirst  and  dis- 
solve sugar.  But  these  are  not  the  characters  which 
it  is  most  convenient  to  begin  with. 

14.  Water  occupies  Space  ;  it  offers  Resist- 
ance; it  has  Weight;  and  is  able  to  transfer 
Motion  which  it  has  acquired;  it  is  therefore 
a  form  of  Matter. 

The  water,  we  see,  fills  the  cavity  of  the  tumbler 
for  half  its  height,  therefore  it  occupies  that  much 
space,  or  has  that  bulk  or  volume.  If  you  put  the 
closed  end  of  another  tumbler  of  almost  the  same  size 
into  the  first,  you  will  find  that  when  it  reaches  the 
water,  the  latter  offers  a  resistance  to  its  going  down, 
and  unless  some  of  the  water  can  get  out,  the  end  of 
the  second  tumbler  will  not  go  in.  Any  one  who  falls 
from  a  height  into  water  will  find  that  he  receives  a 
severe  shock  when  he  reaches  it.  Water  therefore 
offers  resistance. 

If  the  water  is  emptied  out,  the  tumbler  feels  much 


OBJECTS.]  INTRO  DUCTOR  Y. 


lighter  than  it  was  before ;  water,  therefore,  has 
weight. 

And.  finally,  if  you  throw  the  water  out  of  the  tum- 
bler at  any  slightly  supported  object,  the  water  hitting 
against  it  would  knock  it  over.  That  is  to  say,  the 
water  being  put  in  motion  is  able  to  transfer  that 
motion  to  something  else. 

All  these  phenomena,  as  things  which  happen  in 
nature  are  often  called,  are  effects  of  which  water, 
under  the  conditions  mentioned,  is  the  cause,  and  they 
may  therefore  be  said  to  be  properties  (§  4)  of  water. 

All  things  which  occupy  spate,  offer  resistance, 
possess  weight  and  transfer  motion  to  other  things 
when  they  strike  against  them,  are  termed  material 
substances  or  bodies,  or  simply  matter.  Water, 
therefore,  is  a  kind,  or  form,  of  matter. 

15.  Water  is  a  liquid. 

You  will  easily  observe  that,  though  water  occupies 
space,  it  has  no  definite  shape,  but  fits  itself  exactly 
to  the  figure  of  the  vessel  which  holds  it.  If  the 
tumbler  is  cylindrical,  the  contour  of  the  surface  of 
the  water  will  be  circular  when  the  tumbler  is  held 
vertically,  and  will  change,  without  the  hast  break  or 
interruption,  to  more  and.  more  of  an  oval  when  the  tum- 
bler is  inclined  ;  and,  whatever  the  shape  of  the  vessel 
into  which  you  pour  it,  the  sides  of  the  water  always 
exactly  fit  against  the  sides  of  the  vessel.  If  you  put 
your  finger  into  the  water  you  can  move  it  in  all  direc- 
tions with  scarcely  any  feeling  of  obstacle.  If  you 
pull  your  finger  out  there  is  no  hole  left,  the  water  on 
all  sides  rushing  together  to  fill  up  the  space  that  was 
occupied  by  the  finger.  You  cannot  take  up  a  handful  of 


22  SCIENCE  PRIMERS.  [MATERIAL 

water,  for  it  runs  away  between  your  fingers,  and  you 
cannot  raise  it  into  a  permanent  heap.  All  this  shows 
that  the  parts  of  water  move  upon  one  another  with 
great  ease.  The  same  fact  is  illustrated  if  the  tumbler 
is  inclined,  so  that  the  level  of  the  surface  rises  above 
the  edge  of  the  tumbler  on  one  side,  and  the  water  is 
therefore  to  some  extent  unsupported  by  the  tumbler 
at  this  point.  The  water  then  flows  over  in  a  stream 
and  falls  to  the  ground,  where  it  spreads  out  and  runs 
to  the  lowest  accessible  place,  or  gradually  soaks  up 
into  crevices. 

Nevertheless,  although  the  parts  of  the  water  thus 
loosely  slip  and  slide  upon  one  another,  yet  they  hold 
together  to  a  certain  extent.  If  the  surface  of  the 
water  is  just  touched  with  the  finger,  a  little  of  it  will 
adhere ;  and  if  the  finger  is  then  slowly  and  carefully 
raised,  the  adjacent  water  will  be  raised  up  into  a 
slender  column  which  acquires  a  noticeable  length 
before  it  breaks.  So,  in  the  early  morning,  after  heavy 
dew,  you  may  see  the  water  upon  cabbage-leaves  and 
blades  of  grass  in  spherical  drops,  the  parts  of  which 
similarly  hold  together. 

Material  substances,  the  parts  of  which  are  so 
movable  that  they  fit  themselves  exactly  to  the  sides 
of  any  vessel  which  contains  them,  and  which  flow 
when  they  are  not  supported,  are  called  fluids  ;  and 
fluids  the  parts  of  which  do  not  fly  off  from  one 
another,  but  hold  together  as  those  of  water  do,  are 
called  liquids. 

Water  therefore  is  a  liquid. 

16.  Water  is  almost  incompressible. 

It   has   been    seen    that    water,    like    every    other 


OBJECTS.]  INTRO  D  UCTOR  Y. 


material  substance,  resists  the  intrusion  of  other  mat- 
ter into  the  place  which  it  occupies.  But  many  things, 
though  they  resist,  can  be  easily  squeezed  or  com- 
pressed into  a  smaller  volume.  This,  however,  is  not 
the  case  with  water,  which  like  other  liquids,  is  almost 
incompressible  :  that  is  to  say,  an  immense  pres- 
sure is  needful  to  cause  its  volume  to  diminish  to  any 
appreciable  extent.  It  may  seem  strange  that  anything 
so  apparently  yielding  as  water  should  yet  be  almost 
as  difficult  to  squeeze  as  so  much  iron ;  but  the  apparent 
yieldingness  of  water  is  due  to  the  ease  with  which 
it  changes  its  shape  ;  and,  if  water  is  prevented  from 
changing  its  shape,  it  is  very  difficult  to  drive  its  parts 
closer  together.  It  has  been  ascertained  that  if  water 
is  confined  in  a  closed  space,  a  pressure  amounting  to 
fifteen  pounds  on  the  square  inch  diminishes  its  volume 
by  only  Yowo^h  Part-  Take  a  common  syringe,  and 
having  seen  that  the  plug  or  piston  fits  the  cylinder 
of  the  syringe  well,  put  the  nozzle  into  water  and  draw 
the  piston  up.  Then  turn  the  nozzle  upwards  and 
push  upon  the  piston  till  a  little  of  the  water  squirts 
out,  so  as  to  make  sure  that  the  cylinder  contains 
nothing  but  water.  Now  put  your  finger  on  the 
opening  of  the  nozzle  firmly,  so  as  to  stop  any  water 
from  passing  out,  and  then  try  to  push  the  piston  down. 
You  will  find  that  you  cannot  make  it  stir  without  great 
force  ;  and,  if  the  piston  moves  appreciably,  it  will  be 
because  some  of  the  water  has  escaped  by  the  sides 
of  the  piston.  In  fact,  if  the  piston  presented  a  square 
inch  of  surface,  and  fitted  accurately,  and  the  column 
of  water  in  the  cylinder  were  one  inch  long,  it  must 
be  pressed  down  by  a  weight  of  30,000  pounds  (about 
thirteen  tons)  to  make  it  move  one-tenth  of  an  inch. 


24  SCIENCE  PRIMERS.  [MATERIAL 

17.  The  Meaning  of  Weight. 

Let  us  next  consider  the  property  of  weight.  We 
say  that  anything  has  weight  when,  on  trying  to  lift  it 
from  the  ground,  or  on  holding  it  in  the  hand,  we  have 
a  feeling  of  effort.  Or  again,  if  anything  which  is  sup- 
ported at  a  certain  height  above  the  ground,  falls  when 
the  support  is  taken  away,  we  say  that  it  has  weight. 
Now  the  ground  merely  means  the  surface  of  the  earth ; 
and,  as  all  bodies  which  possess  weight  fall  directly  to- 
wards the  surface  of  the  earth  when  they  are  not  kept 
away  from  it  by  some  support,  we  may  say  that  all 
bodies  which  have  weight  tend  to  fall  in  this  way.  And 
it  does  not  matter  on  what  part  of  the  surface  of  the 
earth  you  make  the  experiment.  Rain  consists  of 
drops  of  water,  and  it  does  not  matter  whether  we 
watch  a  shower  in  calm  weather  here,  or  in  New 
Zealand ;  the  drops  fall  perpendicularly  towards  the 
ground.  But  we  know  that  the  earth  is  a  globe  and 
that  New  Zealand  is  at  our  antipodes,  or  on  the 
opposite  side  of  the  globe  to  England.  Hence  if 
two  showers  are  falling  at  the  same  time,  one  in  New 
Zealand  and  one  here — the  drops  must  be  falling  in 
opposite  directions,  towards  one  another ;  that  is, 
towards  the  centre  of  the  earth  which  lies  between 
them.  In  fact,  all  bodies  which  have  weight  tend  to 
fall  towards  the  centre  of  the  earth — that  is  to  say 
they  fall  in  this  way  if  there  is  nothing  to  prevent 
them  ;  and  when  we  speak  of  weight  we  mean  this 
tendency  to  fall.  To  call  anything  heavy,  is  the 
same  as  saying  that  we  fully  expect  that,  if  there  is 
nothing  to  support  it,  it  will  fall  to  the  ground ;  or 
that  if  we  support  it  ourselves  we  shall  be  conscious 
of  effort. 


OBJECTS.]  INTRODUCTORY.  25 

1 8.  Gravity  and  Gravitation. 

The  word  gravity,  when  it  was  lirst  used,  had  ex- 
actly the  same  meaning. as  weight;  and  a  body  which 
lias  weight  is  said  to  gravitate  towards  the  centre  of 
the  earth.  But  gravity  has  now  acquired  a  much 
wider  sense  than  weight.  For  an  immense  number 
of  careful  observations  and  experiments  have  estab- 
lished the  general  rule,  or  law  of  nature,  that  every 
material  substance  tonds  to  approach  every  other 
material  substance,  just  in  the  same  way  as  a  drop  of 
rain  falls  towards  the  earth;  and,  in  fact,  that  any 
two  portions  of  matter,  whatever  the  nature  of  that 
matter  may  be,  will  move  towards  one  another  if  there 
is  nothing  to  prevent  them  from  doing  so. 

To  make  this  clear,  let  us  suppose  that  the  only 
material  bodies  in  the  universe  were  two  spherical  drops 
of  water,  each  a  tenth  of  an  inch  in  diameter.  Each 
of  these  drops  would  have  the  same  bulk  as  the  other, 
and  would  be  a  quantity  of  matter  exactly  equivalent 
to  the  other.  Then,  however  great  the  distance 
which  separated  these  two  drops,  they  would  begin 
to  approach  one  another ;  and,  each  moving  with 
gradually  increasing  swiftness,  they  would  at  length 
meet  in  a  point  exactly  half-way  between  the  positions 
which  they  at  first  occupied.  But  if  the  bulk 
of  one  drop  were  greater  than  that  of  the  other 
drop,  then  the  larger  would  move  more  slowly,  and 
the  point  of  meeting  would  be  by  so  much  nearer 
the  larger  drop.  It  follows  that,  if  the  one  body  of 
water  were  as  big  as  the  earth  and  the  other  remained 
of  its  original  size,  no  bigger  than  a  rain-drop— the 
motion  of  the  large  mass  towards  the  small  one  would 
be  an  inconceivably  minute  fraction  of  the  total 


26  SCIENCE  PRIMERS.  [MATERIAL 

distance  travelled  over.  It  would  appear  as  if  the 
large  body  were  perfectly  still  and  drew  the  small  body 
to  itself. 

This  is  just  what  happens  when  a  single  drop  of 
water  falls  from  a  cloud,  say  through  a  distance 
of  a  mile,  to  the  earth.  The  earth  really  moves 
towards  it,  just  as  it  moves  towards  the  earth,  on 
the  straight  line  which  joins  the  centres  of  the  two. 
But  the  length  of  this  line  which  each  travels  over 
is  inversely  proportional  to  the  quantity  of  matter 
in  each,  that  is  to  say  is  the  less  the  bigger  the  quan- 
tity. So  that  we  have  a  rule-of-three  sum.  As  the 
quantity  of  matter  in  the  earth  is  to  that  in  a  rain- 
drop, so  is  a  mile  to  the  distance  travelled  over  by 
the  earth.  And  if  any  one  worked  out  this  sum,  he 
would  find  that  the  fourth  term  of  the  proportion 
would  be  an  inconceivably  minute  fraction  of  an 
inch.  For  all  practical  purposes,  therefore,  we  may 
consider  the  earth  to  be  at  rest  in  relation  to  all 
falling  bodies,  inasmuch  as  the  quantity  of  matter  in 
any  filling  body  is  insignificant,  in  comparison  with 
that  contained  in  the  earth. 

What  is  true  of  water  is  true,  so  far  as  we  know,  of 
all  kinds  of  matter,  and  we  therefore  say  that  it  is  a 
law  of  nature  that  all  kinds  of  matter  possess  gravity ; 
that  is  to  say,  that  of  any  two,  each  tends  to  move 
towards  the  other,  at  a  speed  which  is  the  slower  the 
greater  the  quantity  of  matter  it  contains  in  propor- 
tion to  that  which  the  other  contains  ;  and  this  speed 
gradually  becomes  quicker  as  the  two  bodies  approach. 

What  is  usually  called  the  law  of  gravitation  is 
a  statement  of  the  same  observed  facts  in  another  and 
more  complete  fashion.  (See  Physics  Primer.} 


OBJECTS.]  INTRODUCTORY.  27 

19.  The  cause  of  Weight:  Attraction: 
Force. 

We  know  nothing  whatever  of  the  reason  why 
bodies  possess  weight.  Bodies  do  not  fall  on  account 
of  the  law  of  gravitation  (§  9) ;  nor  does  their  gravity 
explain  why  they  fall.  Gravity,  as  we  have  seen,  is 
only  a  name  for  weight,  and  the  law  of  gravitation  is 
only  a  statement  of  how  bodies  approach  one  another, 
not  why  they  do  so. 

It  is  often  said  that  gravitation  is  attraction,  and 
that  bodies  fall  to  the  earth  because  the  earth  attracts 
them.  But  the  word  "  attract "  simply  means  to  "  draw 
towards,"  and  " attraction"  means  nothing  but  "draw- 
ing towards ; "  and  to  say,  when  two  bodies  move  to- 
wards one  another,  that  they  are  "  drawn  towards  "  one 
another,  is  simply  to  describe  the  fact  and  makes  us 
no  whit  wiser  than  we  were  before.  On  the  contrary, 
unless  we  take  great  care,  it  may  make  us  a  little  less 
wise.  For  the  words  "  drawing  towards  "  are  so  closely 
associated  with  ropes  and  hooks  and  the  act  of  pulling, 
that  we  are  easily  led  to  fancy  the  existence  of  some 
analogous  invisible  machinery  in  the  case  of  mutually 
attractive  bodies. 

Again,  gravitation  is  spoken  of  as  a  force ;  and 
as  the  word  force  is  in  vory  common  use,  let  us  try  to 
make  out  what  we  mean  by  it.  A  man  is  said  to  exert 
force  when  he  pushes  or  pulls  anything  so  as  either  to 
exert  pressure  upon  it  or  to  put  it  in  motion.  A 
wrestler's  force  is  proved  by  his  hug  ;  a  bowler's  force 
is  shown  by  the  swiftness  of  motion  of  the  ball. 

Force,  then,  is  the  name  which  we  give  to  that 
which  causes  or,  in  the  case  of  pressure,  tends  to 
cause,  motion.  The  force  of  gravity  therefore  means 


28  SCIENCE  PRIMERS.  [MATERIAL 

the  cause  of  the  pressure  which  we  feel  when  bodies 
which  possess  gravity  are  supported  by  our  bodies, 
and  the  cause  of  their  movement  towards  the  centre 
of  the  earth,  when  they  are  free  to  move.  But  it  is 
exactly  about  the  cause  of  these  phenomena  that  we 
know  nothing  whatever. 

A  good  deal  of  mischief  is  done  by  the  inaccurate  use 
of  such  words  as  attraction  and  force,  as  if  they  were 
the  names  of  things  having  an  existence  apart  from 
natural  objects,  and  from  the  series  of  causes  and  effects 
which  are  open  to  our  observation ;  while  they  are,  in 
reality,  merely  the  names  of  the  unknown  causes  of 
certain  phenomena.  And  it  is  worth  while  to  take 
pains  to  get  clear  ideas  on  this  head  at  the  outset  of 
the  study  of  science. 

Let  us  remember  then  that,  so  far  as  we  know,  it  is 
a  law  of  nature,  that  any  two  material  bodies,  if  they 
are  free  to  move,  approach  one  another  with  gra- 
dually increasing  swiftness ;  and  that  the  space  over 
which  each  travels  before  the  two  meet,  is  inversely  pro- 
portional to  the  quantity  of  matter  which  it  contains. 
Attraction  of  gravitation  is  a  name  for  this  gene- 
ral fact ;  weight  is  the  name  for  the  fact  in  the  case 
of  terrestrial  bodies ;  force  is  a  name  which  we  give 
to  the  unknown  cause  of  the  fact.  The  fact  is  that 
which  it  is  important  to  know.  The  names  are  of  no 
great  consequence  so  long  as  we  recollect  that  they 
are  merely  names  and  not  things. 

20.  The  Weight  of  Water  is  Proportioned 
to  its  Bulk. 

We  must  next  consider,  not  weight  in  general,  but 
the  weight  of  water.  We  say  that  a  tumbler  full  of 


OBJECTS.]  INTRODUCTORY.  29 

water  is  heavier  than  an  empty  tumbler,  because  the 
full  tumbler  gives  us  a  greater  feeling  of  effort  when 
we  lift  it  than  the  empty  tumbler  does.  The  more 
water  there  is  in  the  tumbler  the  greater  is  the  effort. 
A  pail  full  of  water  requires  still  more  effort,  though 
the  empty  pail  feels  quite  light :  and,  when  we  come  to 
deal  with  a  large  tub  full  of  water,  we  may  be  unable 
to  stir  it,  though  the  empty  tub  could  be  lifted  with 
ease.  Thus  it  seems  that  the  greater  the  bulk  of 
water  the  more  it  weighs,  and  the  less  the  bulk  the 
less  it  weighs.  But  then  a  single  drop  of  water  in  the 
palm  of  the  hand  seems  to  weigh  nothing  at  all. 
However,  this  clearly  cannot  be,  for  the  drop  falls  to 
the  ground  readily,  and  therefore  it  must  have  weight. 
Moreover,  a  few  thousand  drops  would  fill  the  tumbler, 
and  if  a  thousand  drops  weigh  something,  each  drop 
must  have  a  thousandth  of  that  weight.  The  fact  is 
that  our  feeling  of  effort  is  a  very  rough  measure  of 
weight,  and  does  not  enable  us  to  compare  small 
weights,  or  even  to  perceive  them  if  they  are  very 
small.  To  know  anything  accurately  about  weight 
we  must  have  recourse  to  an  instrument  which  is 
contrived  for  the  purpose  of  measuring  weights  with 
precision. 

21.  The  Measuring  of  Weights.  The 
Balance. 

Such  an  instrument  is  the  balance  or  scales,  which 
you  may  see  in  every  grocer's  shop.  It  is  composed 
of  a  beam  which  moves  easily  on  a  pivot  fixed  to  its 
middle,  and  which  has  a  scale-pan  attached  to  each 
end.  So  long  as  both  scale-pans  are  empty  the  beam 
is  horizontal ;  but  if  you  put  anything  which  has 


30  SCIENCE  2>RIMERS.  [MATERIAL 

weight  into  one,  that  one  goes  down  and  the  other 
rises.  If  now  you  either  pull  or  push  the  empty 
scale  downwards,  the  beam  may  be  brought  into  the 
horizontal  position  again,  and  the  effort  required  to 
bring  it  into  the  horizontal  position  will  be  the 
greater,  the  greater  the  weight  of  the  body  in  the 
opposite  scale.  An  ounce  in  the  one  scale  is  easily 
raised  by  the  pressure  of  a  ringer  in  the  other.  A 
pound  requires  more  effort;  ten  pounds  needs  put- 
ting out  the  strength  of  the  arm  ;  to  raise  fifty  pounds 
involves  still  more  exertion  ;  while  a  couple  of  hundred- 
weight will  not  be  stirred  by  the  strongest  push  or  pull 
upon  the  empty  scale. 

Suppose  that,  instead  of  pressing  down  the  empty 
scale,  you  put  something  that  has  weight  into  it; 
then,  as  soon  as  this  weight  is  equal  to  that  in  the 
other  scale,  the  beam  will  become  horizontal.  In  fact, 
one  scale  has  just  as  much  tendency  to  move  towards 
the  centre  of  the  earth  as  the  other  has,  and  as  neither 
can  go  down  without  pulling  the  other  up,  they  neu- 
tralise one  another.  It  comes  to  the  same  thing,  as  if 
two  boys  of  equal  strength  were  pulling  one  against 
the  other ;  so  long  as  the  pulls  in  opposite  directions 
are  equal,  of  course  neither  boy  can  stir ;  while  the 
smallest  addition  of  strength  to  one  enables  him  to 
pull  the  other  over. 

22.  The  "Weight  of  the  same  Bulk  or 
Volume  of  Water  is  Constant  under  the  same 
conditions.  Mass.  Density. 

Now  let  two  graduated  thin  glass  measures  be  put 
into  the  two  scales,  and  made  to  counterpoise  one 
another  exactly.  Then,  if  even  a  single  drop  of 


OBJECTS.]  INTRODUCTORY.  3* 

water  is  put  into  the  one  measure  the  scale  will 
descend,  if  the  balance  is  a  good  one ;  showing  that 
the  drop  has  weight.  If  the  measures  are  graduated 
accurately,  then  whatever  volume  of  water  is  put  into 
one,  an  exactly  similar  volume  of  the  same  water  must 
be  put  into  the  other  to  make  the  beam  level.  This 
obviously  means  that  the  same  volume  of  water 
under  the  same  circumstances  always  has 
the  same  weight. 

In  §  18  it  was  said  that  bodies  tend  to  move  to- 
wards one  another  with  a  relative  velocity 1  which  is 
inversely  proportional  to  the  quantity  of  matter  which 
they  contain.  But  how  are  we  to  measure  quantity  of 
matter?  Is  it  to  be  estimated  by  the  space  which  it 
occupies ;  that  is,  by  its  volume  ?  or  are  we  to  esti- 
mate ihe  quantity  of  matter  in  a  body  by  its  weight  ? 
You  will  soon  learn  that  the  volume  of  all  bodies 
is  constantly  changing  in  correspondence  with  the 
changes  in  the  pressure  exerted  by  other  bodies,  but 
more  especially  in  correspondence  with  the  changes 
of  temperature  to  which  they  are  subjected  ;  while 
the  weight  of  the  same  body,  at  the  same  point  on 
the  earth's  surface,  never  alters.  Hence  we  may 
take  the  weight  of  a  body  as  a  measure  of  the  quantity 
of  matter  which  it  contains ;  and  it  follows  that,  for  the 
same  weight,  the  larger  the  volume  of  a  body  the  less 
matter  it  contains  proportionally  to  its  volume,  and 
the  less  the  volume,  the  more  matter  it  contains.  The 

1  Velocity,  or  swiftness,  is  measured  by  the  distance  over  which 
a  body  travels  in  a  given  time.      Of  two  bo  ies,  one  of  which 
travels  through  one  foot  in  a  second,  while  the  other  travels 
through  two  feet,  the  latter  has  the  greater  relative  velocity. 
3* 


32  SCIENCE  PRIMERS.  [MATERIAL 

proportion  of  its  weight  to  its  volume  gives  us  the 
density  of  a  body. 

Now  what  is  true  of  water  is  true  of  all  other  bodies 
or  material  substances.  Suppose  that  one  of  the 
measures  is  emptied  and  replaced,  the  beam  may  be 
brought  to  the  horizontal  position  again  by  means  of 
a  piece  of  lead  cut  to  exactly  the  right  size.  The 
piece  of  lead  will  thenceforth  furnish  an  exactly  cor- 
responding or  equivalent  weight  for  so  much  water ; 
and  pieces  of  iron  or  brass,  which  counterpoise  the 
lead,  will  also  be  equivalents  of  the  weight  of  the  water, 
or  of  the  lead,  or  of  one  another.  But  the  pieces  of 
lead,  iron,  or  brass  will  obviously  be  of  much  less 
volume  or  bulk  than  the  water  which  they  counterpoise. 
Here  it  follows  that  the  densities  of  these  metals,  or 
the  quantity  of  matter  contained  in  the  same  volume, 
must  be  much  greater  than  in  the  case  <of  water. 

What  are  called  weights  in  commerce  are  pieces  of 
lead,  or  iron,  or  brass  exactly  equivalent  in  weight  to  a 
certain  bulk  of  water  under  certain  conditions.  An 
imperial  gallon  of  water  thus  weighs  ten 
pounds,  and  therefore  an  imperial  pint 
weighs  a  pound  and  a  quarter. 

23.  Equal  Volumes  of  Different  Things 
under  the  same  circumstances,  have  Different 
Weights  :  the  Density  of  Different  Bodies  is 
Different. 

The  important  fact  which  has  just  been  alluded  to 
must  be  considered  more  fully.  We  have  seen  that 
an  imperial  pint  measure  gives  us  the  space  which  is 
taken  up  by  as  much  water  as  weighs  a  pound  and  a 
quarter;  and  this  space  is  the  bulk  or  volume  of  that 


OBJECTS.]  INTRODUCTORY.  33 

weight  of  water.  But  if  you  take  an  ordinary  pound 
weight  and  a  quarter-pound  weight,  and  put  them  into 
an  imperial  pint  measure,  you  will  find  that,  instead  of 
filling  it,  they  take  up  only. a  very  small  portion  of  the 
space  in  its  interior,  or  in  other  words,  of  its  capacity. 
Thus  the  volume  of  a  pound  and  a  quarter  of  lead,  or 
of  iron,  or  of  brass,  is  very  much  less  than  the  volume  ' 
of  the  same  weight  of  water ;  that  is  to  say,  the  metals 
are  denser  than  water  ;  the  same  volume  has  greater 
mass  or  more  gravity.  Or,  to  put  the  case  in  another 
way,  fill  the  tumbler  with  which  we  began  half  full  of 
water,  making  a  mark  on  the  side  exactly  at  the  level 
of  the  top  of  the  water.  Then  place  it  in  one  scale  of  a 
balance,  and  counterpoise  it  with  weights  in  the  other. 
Next,  pour  out  the  water,  and  after  drying  the 
tumbler,  fill  it  with  fine  sand  carefully  up  to  the  mark. 
The  volume  of  sand  will  be  equal  to  the  volume  of 
water.  But  now  the  same  weights  will  no  longer 
counterpoise  it,  and  you  will  have  to  put  more 
weights  in  the  opposite  scale.  Volume  for  volume, 
therefore,  sand  is  heavier  than  water.  Throw  out  the 
sand,  and  put  in  sawdust  in  the  same  way,  and  you 
will  find  that  a  less  weight  than  was  necessary  to 
counterpoise  the  water  counterpoises  the  sawdust. 
Volume  for  volume,  therefore,  sawdust  is  lighter  than 
water.  Experiment  in  the  same  way  with  spirit  and 
oil,  and  they  will  be  found  to  be  lighter  than  water, 
while  treacle  will  be  heavier,  and  quicksilver  very 
much  heavier  than  water. 

24.   The  Meaning  of  Heavy   and   Light — 
Specific  Gravity. 

We  are  in  the  habit  of  using  the  words  heavy  and 


34  SCIENCE  PRIMERS.  [MATERIAL 

light  rather  carelessly.  We  call  things  that  are  easily 
lifted  light,  and  things  that  are  hard  to  lift,  heavy. 
We  say  that  sand,  which  is  blown  about  by  the  wind, 
is  light,  and  that  a  block  of  wood  is  heavy,  and  yet 
we  have  just  seen  that  sand  is  heavier,  bulk  for 
bulk,  than  wood.  In  order  to  get  rid  of  this 
double  meaning,  the  weight  of  a  volume  of  any 
liquid  or  solid,  in  proportion  to  the  weight  of  the 
same  volume  of  water  at  a  known  temperature  and 
pressure,  is  called  its  specific  gravity.  Water  being 
taken  as  i,  anything  a  volume  of  which  is  twice  as 
heavy  as  the  same  volume  of  water  is  said  to  have 
the  specific  gravity  2  :  if  three  times,  3 ;  if  four  and  a 
half  times,  4/5,  and  so  on.  Thus  the  specific  gravity 
of  any  liquid  or  solid  expresses  its  density  in  pro- 
portion to  that  of  water  under  the  same  conditions. 
Sawdust,  oil,  and  spirit  have  a  less  specific  gravity  than 
water,  while  treacle,  sand,  and  quicksilver  have  a 
greater  specific  gravity.  In  this  sense,  the  former 
three  substances  are  light,  while  the  latter  three  are 
heavy. 

25.  Things  of  greater  Specific  Gravity 
than  Water  sink  in  Water ;  Things  of  less 
Specific  Gravity  float. 

Here  are  two  tumblers  of  water.  Throw  some 
sand  into  one  and  some  sawdust  into  the  other. 
What  happens  ?  The  sand  sinks  to  the  bottom,  the 
sawdust  floats  at  the  top.  We  may  stir  them  up  as 
we  like,  but  the  sand  will  tumble  to  the  bottom  and 
the  sawdust,  as  obstinately,  rise  to  the  top.  Thus 
that  which  is  lighter  than  the  water  floats,  and  that 
which  is  heavier  (bulk  for  bulk)  sinks.  So,  if  we  pour 


OBJECTS.]  INTRODUCTORY.  35 

some  oil  into  the  water,  it  floats,  and  if  we  pour  some 
coloured  spirit  in  carefully,  it  also  floats  ;  while  treacle 
and  quicksilver  sink  to  the  bottom,  just  as  the  iron- 
filings  do. 

We  saw  that  the  iron-filings  sank,  because  iron  is 
heavier  than  water.  Here  is  a  piece  of  the  thin  tinned 
sheet-iron  that  they  make  tin  boxes  of.  What  will 
happen  if  we  drop  it  into  the  water?  It  is  heavier 
than  water,  bulk  for  bulk,  and  therefore  it  will  sink  as 
you  see  it  does. 

But  now  here  is  a  "  tin"  canister  made  of  this  very 
same  tinned  sheet-iron.  We  drop  that  into  the  water, 
and  you  see  it  does  not  sink  at  all,  but  floats  at  the 
top  as  if  it  were  made  of  cork.  Here  is  a  perplexity. 
We  were  sure  just  now  that  iron  is  heavier  than  water, 
and  here  is  an  iron  box  floating  !  Is  this  an  exception 
to  the  law  ?  Not  at  all ;  for  what  we  said  was  that  a 
thing  would  float  if  it  were  lighter,  bulk  for  bulk, 
than  water.  Now  let  us  weigh  the  tin  box,  and  having 
weighed  it  let  us  next  try  to  find  out  how  much  the 
same  bulk  of  water  weighs.  This  may  be  done  very 
simply,  for  the  walls  of  the  box  are  very  thin,  so  that 
the  inside  of  the  box  is  very  nearly  as  large  as  the 
whole  box.  Consequently,  if  we  fill  the  box  with 
water,  and  then  weigh  the  water,  we  shall  find  out, 
very  nearly,  what  is  the  weight  of  a  bulk  of  water  as 
great  as  that  of  the  box.  But  if  we  do  this,  we  shall 
find  that  the  water  which  was  contained  in  the  box, 
weighs  very  much  more  than  the  box  does.  So  that, 
bulk  for  bulk,  the  box,  although  it  is  made  of  iron, 
is  really  lighter  than  water,  and  that  is  why  it  floats. 

You  will  all  have  heard  of  the  iron  ships  which  are 
now  so  common,  and  you  may  have  wondered  how  it 
4 


36  SCIENCE  PRIMERS.  [.MATERIAL 


is,  that  ships  made  of  thick  ^  plates  of  iron  riveted 
together,  and  weighing  many  thousand  tons,  do  not 
gt>  to  the  bottom.  But  they  are  nothing  but  our  tin 
canisters  on  a  great  scale,  and  they  flout  because  each 
ship  weighs  less  than  a  quantity  of  water  of  the  same 
bulk  does. 

It  is  because  of  this  property  of  water  to  bear  up 
things  lighter  than  itself,  and  because  of  that  other 
property  of  being  easily  moved  which  the  particles  of 
water  , have,  that  the  sea,  and  rivers,  and  canals,  are 
such  great  highways  for  mankind. 

For  there  is  nothing  so  heavy  that  it  may  not  be 
made  to  float  in  water,  if  the  box  which  holds  it  is 
large  enough  to  make  the  weight  of  the  whole  less 
than  the  weight  of  the  same  bulk  of  water.  And 
then,  having  once  got  the  weight  to  float,  the  particles 
of  water  are,  so  easily  moved,  that  the  force  of  the 
winds,  or  of  oars,  or  of  paddles,  readily  causes  it  to 
slip  through  the  water  from  one  place  to  another. 

26.  A  Body  which  Floats  in  Water  always 
occupies  as  much  Space  beneath  the  level  of 
the  Surface  of  the  Water  as  is  equal  to  the 
Volume  of  Water  which  weighs  as  much  as 
that  Body ;  in  other  words,  it  displaces  its 
own  Weight  of  Water. 

A  cubic  inch  of  water  weighs  about  252  grains  and  a 
half.  Suppose  that  the  t'.n  box  in  the  previous  experi- 
ment was  square,  and  had  the  bulk  of  100  cubic  inches, 
then  the  weight  of  a  corresponding  volume  of  water 
would  be  25,250  grains.  If  the  box  weighed  8,416 
grains,  just  a  third  of  its  bulk  would  be  immersed  ;  if 


OBJECTS.]  INTRODUCTORY.  37 

12,625  grains,  half;  if  16,832  grains,  it  would  sink  two  - 
thirds  of  its  volume,  and  so  on.  Or,  if,  when  the  box! 
is  floating,  you  make  a  mark  upon  its  side  at  the  exact 
level  of  the  surface  of  the  water,  the  bulk  of  that 
portion  of  the  box  which  lies  below  the  water-level 
can  be  ascertained.  Suppose  it  to  be  thirty  cubic 
inches,  then  the  weight  of  the  box  will  be  30X252-5 
or  7575  grains.  Hence  it  may  be  said  that  the  im- 
mersed part  of  a  floating  body  takes  the  place  of  the 
water  which  it  displaces,  and,  as  it  were,  represents 
it.  If  you  press  downwards  upon  the  floating  box, 
there  is  a  feeling  of  resistance  as  it  descends,  and 
when  the  pressure  is  taken  off,  the  body  immediately 
rises  again.  Hence  the  water  presses  upwards  against 
the  bottom  of  the  floating  boHy.  But  it  also  presses 
against  the  sides,  for  if  the  sides  of  the  box  are  very 
thin  they  will  be  driven  in.  If  a  thin  empty  bottle  is 
tightly  corked  and  lowered  into  deep  water  the  cork 
will  be  driven  in,  or  else  the  bottle  will  be  crushed. 

27.  Water  Presses  in  all  Directions. 

Thus  water  presses  in  all  directions  upon  things 
which  are  immersed  in  it. 

If  a  long  wooden  or  metal  pipe,  placed  vertically, 
has  its  lower  end  stopped  with  a  cork  which  does  not 
fit  very  tightly,  and  water  is  poured  into  the  top  of  the 
tube,  the  water  will  at  first  fill  the  part  of  the  tube 
above  the  cork,  and  its  weight  will  exert  a  certain 
pressure  on  the  cork.  In  fact,  if  the  end  of  the 
tube  is  stopped  by  applying  the  palm  of  the  hand 
closley  against  it,  the  downward  pressure  of  the 
water  will  have  to  be  overcome  by  a  certain  amount 
of  effort.  As  the  water  accumulate's,  This  .dawn ward , 

OF 


38  SCIENCE  PRIMERS.  [MATERIAL 

pressure  will  become  greater  and  greater  until  the 
hand  is  driven  away,  or  the  cork  is  forced  out,  and  the 
water  falls  to  the  ground.  The  pressure  in  this  case 
is  the  same  as  the  weight  of  the  water,  and  the  cork 
would  have  been  driven  out  equally  well  by  a  rod  of 
lead  of  the  same  weight. 

Suppose  the  tube  to  be  square,  and  that  the  inside 
of  the  square  measures  exactly  one  inch  each  way. 
Then  an  inch  of  height  of  the  tube  will  hold  exactly 
one  cubic  inch  of  water.  Since  one  cubic  inch  of 
water  weighs  252  grains  and  a  half,  as  much  water 
as  will  fill  the  tube  about  two  feet  three  inches 
and  a  half  high,  will  weigh  a  pound  (7,000  grains), 
and  fifteen  pounds  of  water  will  fill  such  a  tube 
between  thirty-three  and  thirty-four  feet  high.  And 
these  respective  weights  measure  the  pressure  of  two 
columns  of  water,  one  twenty-seven  and  a  half  inches 
high,  and  the  other  nearly  thirty-four  feet  high,  on  a 
square  inch  of  the  surface  on  which  they  rest. 

The  specific  gravity  (§  24)  of  lead  is  11*45;  in 
other  words  it  is  about  eleven  and  a  half  times  denser 
than  water.  Therefore  if  a  bar  of  Ic^d  cut  square 
and  one  inch  in  the  side,  and  rather  less  than  T\th 
of  the  height  of  a  column  of  water,  is  slipped  into 
the  tube  in  place  of  the  water,  it  will  exert  the  same 
pressure  on  the  bottom. 

And  now  comes  a  difference  between  the  lead 
and  the  water,  which  depends  on  the  fluidity  of  the 
latter.  The  lead  exerts  no  pressure  on  the  sides  of 
the  tube,  but  the  water  does.  If  a  small  hole  is  cut 
in  the  side  of  the  tube  close  to  the  bottom,  and 
stopped  with  a  cork,  the  lead  will  not  press  upon 
the  cork.  But  if  the  column  of  water  is  high  enough, 


OBJECTS.]    I  INTRODUCTOR  Y.  39 

the  cork  will  be  driven  out  with  as  much  force  as 
before,  so  that  the  water  presses  just  as  much  side- 
ways as  downwards.  Jt  is  osy  to  satisfy  oneself  of, 
this  by  inserting  a  long  glass  tube,  with  .-its  lower  end 
bent  at  right  angles  and  fitted  with  a  cork,  into  tl  e 
side  of  the  wooden  pipe.  The  water  will  at  once 
rise  in  the  tube  to; the  same  height  as  it  has  in  the" 
pipe.  Whence  it  is  6bvious  that  the  pressure  of  the 
water  on  any  point  of  the  side  is;  exactly  equal  to  the 
vertical  pressure  at  that  poiht;  for  the  pressure  outwards 
is  exactly  balanced  by  that  of  the  vertical  column  in 
the  tube  inwards.  The  water  in  a  watering-pot  always 
stands  at  the  sameclevel  in  the  can  and  in  the  spout. 

If  a  glass  tube  is  bent  into  the  shape  of  a  (J>  an^ 
water  is  poured  into  it,  the  water  will  always  stand  at, 
the  same  level  in  the  two  legs  of  the  tube,  whatever 
the  shape  of  the  bend  may  be,  or  the  relative  capa- 
cities of  the  two  legs,  or  the  inclination  of  the  tube. 
,  And  this  must  needs  be  so,  for  the  force  with  which 
the  water  tends  to  flow  out  of  the  one  half  of  the 
^arrangement  depends  on  the  vertical  height1  of  the  sur- 
face of  the  water  abc-ve  the  aperture  of  exit;  $o  that 
any  column  of  equal  vertical  height  must  balance  it. 

That  a  column  of  watei  will  stand  at  exactly  the 
same  level  as  any  other  with  which  it  communicates, 
may  be  seen  still  more  simply  by  placing  a  glass  tube, 
open  at  each  end,  in  a  Basin  of  water.  However  the 
tube  may  be  inclined  or  bent,  whether  its  lower  end  is 

1  Vertical  height  is  the  height  measured  along  a  line  drawn 
from  the  surLce  of  the  water  perpendicularly  to  the  s  urface  of  the 
earth.  A  plumb-line  is.  a  string  to  one  end  of  which  a  weight 
is  attached  and  thus  hangs  suspended.  If  the  other  end  of  the  line 
is  brought  opposite  the  surface  of  the  water  the  direction  of 
the  string  answers  to  the  line  of  vcrt'cal  height,  it~ 


4o  SCIENCE  PRIMERS.  [MATERIAL 

wicb  or  narrow,  the  column  of  water  inside  it  will  be  at 
exactly  the  same  level  as  the  water  outside  it.  Yet,  of 
course,  the  rigid  glass  walls  of  the  tube  cut  off  all 
communication  between  the  column  of  water  inside 
it  and  the  rest,  except  at  the  bottom. 

In  a  well-ordered  town,  water  is  supplied  to  every 
house  and  can  be  drawn  from  taps  placed  in  the 
highest  stories.  These  are  fed  by  pipes  which  lead 
from  a  cistern  at  the  top  of  the  house.  This  water  is 
brought  from  a  large  pipe,  or  main,  in  the  street,  by 
a  smaller  house-pipe,  which  is  often  made  to  twist 
about  in  various  directions  before  it  reaches  the 
cistern  at  the  top  of  the  house  into  which  it  delivers 
the  water.  If  you  followed  the  main,  you  would  find 
that  it  took  a  long  course  up  and  down,  beneath  the 
pavement  of  the  streets,  until  at  last  it  reached  the 
waterworks.  Here  you  would  find  that  the  main 
was  connected  with  a  reservoir ;  and  either  this  reser- 
voir is  at  a  greater  height  than  any  of  the  cisterns 
into  which  the  water  is  delivered,  or  there  is  some 
means  of  pumping  the  water  from  it  to  that  height  on  - 
its  way  to  the  main.  Thus  the  reservoir,  the  main, 
and  the  house-pipe  form  one  immense  (J-tube,  anc^ 
the  water  in  the  house-pipe  tends  to  rise  to  the  same 
level  as  that  of  the  water  in  the  reservoir,  and  hence 
flows  into  the  cistern  when  the  supply-pipe  is  open. 

28.  The  Transference  of  Motion  by  Moving 
Water:  the  Momentum  of  Moving  Water. 

Suppose  a  wooden  vat  with   a  horizontal  tap,  the 
sectional  a'rea1  of  the  tube  of  which  is  one  square  inch, 

1  The  Factional  area  of  a  tube  is  the  surface  occupied  by  its 
cavity  when  it  is  cut  across.       It  \vould  be  represented  by  the 


OBJECTS.]  INTRODUCTORY.  4l 

inserted  close  to  the  bottom,  to  be  filled  with  water 
up  to  100  inches  above  the  tap.  Then  supposing  the 
tap  to  be  shut,  the  pressure  upon  its  sectional  area  will 
be  25,250  grains,  or  rather  more  than  three  pounds 
and  a  half — and  there  is  the  same  pressure  on  every 
square  inch  of  the  bottom  of  the  vat. 

If  the  tap  is  now  turned,  the  water  nearest  to  it 
being  unsupported  on  its  outer  side,  the  pressure  on 
the  inner  side  sets  it  in  moiion,  and  it  ilows  out  in  a 
stream.  At  first  the  stream  shoots  out  violently  and 
the  water  is  carried  to  a  long  distance.  That  is  to 
say,  the  weight  of  the  column  of  water  100  inches 
high  acts  as  a  force,  or  cause  of  motion,  upon  thj 
water  nearest  the  tap,  and  this  water  i.3  forced  out 
with  a  velocity  depending  on  that  force  in  a 
horizontal  direction.  Now  suppose  that  you  take  a 
common  toy  cup-and-ball  and  bring  the  ball  into  llie 
way  of  the  stream  of  water.  The  stream  will  at  oncj 
strike  the  ball  and  drive  it  in  the  same  direction  as 
that  which  it  is  itsjlf  taking.  The  power  which  the 
moving  water  has  of  transferring  or  communicating 
motion  to  a  body  which  is  at  rest,  but  free  to  move 
as  the  ball  is,  is  due  to  its  momentum.  The 
greater  the  mass  of  the  stream  and  the  more  rapidly 
it  moves,  the  more  motion  will  it  communicate  to  the 
ball,  or  the  heavier  the  ball  it  will  move.  Close  to 
the  mouth  of  the  tap  the  direction  of  the  stream  is 
horizontal;  but  it  very  soon  begins  to  bend  down- 
wards, and  describing  a  rapid  curve,  comes  to  the 
ground.  It  does  this  for  just  the  same  reasons  that 
a  stone  thrown  horizontally  describes  a  curve,  and  at 

surface  of  a  piece  of  cardboard,  like  the  wad  of  a  gun,  just 
large  enough  to  go  into  the  tube. 


42  SCIENCE  PRIMERS.  [MATERIAL' 

length  strikes  the  ground  ;  and,  in  fact,  the  stream  may 
be  regarded  as  so  much  water  thrown  horizontally. 

These  reasons  are  two  :  firstly,  as  soon  as  the  water 
has  left  the  tap  it  is  an  unsupported  heavy  body  ;  and, 
as  such,  it  begins  to  fall  to  the  ground.  Secondly,  the 
momentum  of  the  water  is  continually  being  dimi- 
nished by  the  resistance  .of  the  air  through  which  it 
passes.  For,  although  the  air  which  surrounds  us  is 
so  thin,  and  movable,  a  body  that  we  ordinarily  take 
no  notice  of  it — the  fact  that  it  offers  resistance  to 
bodies  which  move  through  it  is  easily  observed; 
as,  for  example,  in  using  a  fan.  The  water  has  to 
overcome  this  resistance,  and  its  momentum  is 
proportionally  diminished. 

j&  If,  when  the  water  leaves  the  tap,  the  air  and  gravi- 
tation were  alike  abolished,  the  water,  keeping  its 
momentum,  would  travel  for  ever  in,  the  same 
direction. 

As  the  water  runs  out,  it  will  be  observed  that  the 
velocity  of  the  stream  becomes  less  and  the  curve* 
which  it  describes  sharper,  so  that  it  comes  to  the 
ground  sooner;  and  finally,  when  the  vat  is  nearly 
empty,,  the  stream  falls  nearly  vertically  downwards. 
The  reason  of  this  is  that  the  level  of  the  top  of 
the  water  is  gradually  lowered;  consequently,  the 
height  of; the  column  which  presses  on  the  water  close 
to  the  tap  is  gradually  lessened,  and  therefore  its 
weight  is  diminished.  But  this  weight  or  pressure 
is  the  cause  of  the  motion  of  the  water,  and  as  the 
cause  diminishes  the  effect  of  that  cause  must  diminish, 
Therefore  the  momentum  of  the  water  is  gradually 
lessened  and  it  is  carried  less  and  less  far  horizontally 
in  the  ^ time  which  it  takes  to  fall  to  the  ground;. 


OBJECTS.]  INTRODUCTORY.  43 

until  finally,  it  acquires  no  appreciable  horizontal 
motion  at  all,  and  so  falls  vertically  downwards  from 
the  mouth  of  the  tap. 

29.  The  Energy  of  Moving  Water. 

If  a  short  pipe  bent  at  right-angles  like  the  letter 
L  is  fitted  by  one  arm  on  to  the  end  of  the  tap, 
while  the  other  is  turned  vertically  upwards,  and  the 
vat  is  full  as  before;  when  the  tap  is  turned,  the 
water  will  shoot  up  into  the  air,  and  after  rising  for  a 
certain  distance  will  stop,  and  then  fall.  In  fact  we 
shall  have  a  fountain. 

Observe  the  difference  between  the  vertical  jet  of 
water  and  the  horizontal  jet.  If  we  leave  the  resist- 
ance of  the  air  out  of  consideration,  the  water  in  the 
horizontal  jet  has  no  obstacle  to  overcome ;  and  it  might 
go  on  for  ever,  if  its  weight  did  not  gradually  cause 
its  path  to  become  more  and  more  bent  towards  the 
earth,  against  which  it  eventually  strikes. 

When  the  jet  is  vertical  the  case  is  altered.  The 
water  thrown  up  vertically  constantly  tends  to  fall 
down  vertically,  as  any  other  heavy  body  would  do, 
and  its  momentum  has  to  overcome  the  obstacle  of 
its  gravity.  Any  given  portion  of  the  water  is,  in  fact, 
acted  upon  by  two  opposite  tendencies,  momentum 
urging  it  up,  and  gravity  pulling  it  down.  Now  if  two 
equal  tendencies  exactly  oppose  one  another,  the  body 
upon  which  they  act  does  not  move  at  all ;  while,  if 
one  is  stronger  than  the  other,  the  body  moves  in  tlu 
direction  of  the  stronger. 

Thus  a  portion  of  water  which  has  just  left  the 
spout  shoots  up,  because  the  velocity  with  which  it  is 
impelled  upwards  is  sufficient  to  carry  it  through  a 


44  SCIENCE  PRIMERS.  [MATERIAL 

greater  space  in  a  given  time,  say  a  second,  than  that 
through  which  its  gravity  would,  in  the  same  time, 
impgl  it  downwards. 

But  the  distance  which  the  water  will  travel  during 
this  second  will  be  the  difference  between  the  distance 
which  it  would  have  ascended  if  there  had  beeii-no 
gravity  forcing  it  down,  and  the  distance  which  it 
would  have  descended  if  there  had  been  no  momentum 
driving  it  up  ;  and,  at  the  end  of  the  second,  the  rate  of 
its  motion  upwards,  or  its  velocity,  will  be  proportion- 
ally slower.  Thus,  at  the  end  of  the  first  second,  the 
water  has  spent  a  certain  portion  of  its  momentum  in 
overcoming  its  gravity.  And  as  there  is  nothing  to 
make  good  the  loss,  it  would,  if  left  to  itself,  travel 
more  slowly,  or  over  a  less  distance,  in  the  second 
second  than  it  tended  to  do  in  the  first.  But  though 
the  momentum  of  the  water  is  diminished,  its  gravity, 
weight,  or  tendency  to  fall  downwards,  for  a  given 
distance  in  a  second,  remains  exactly  what  it  was,  and 
operates  in  the  course  of  the  second  second  to  exactly 
the  same  extent  as  in  the  first.  Hence,  at  the  end  of 
the  second  second,  the  distance  through  which  the 
water  travels  upwards  is  still  smaller,  and  its  velocity 
is  still  more  diminished.  It  is  obvious  that,  however 
great  the  disproportion  between  momentum  and  gravity 
to  start  with,  gravity  must  gain  the  day  in  the  long  run 
under  these  circumstances.  The  store  of  momentum 
will  be  usad  up ;  and,  after  a  momentary  rest,  the 
water,  reduced  to  the  condition  of  a  body  without 
support,  will  begin  to  be  carried  downwards  by  the 
unopposed  action  of  gravity. 

The  case  is  similar  to  that  of  a  boy  sculling  a  boat, 
the  bows  of  which  are  suddenly  seized  and  the  boat 


OBJECTS.]  INTRODUCTORY.  %    45 

thrust  violently  backwards  by  a  strong  man.  The 
boat  will  go  stern  foremost  rapidly,  at  first,  but  every 
stroke  of  the  boy's  oar  at  the  stern  will  retard  its  back- 
ward motion ;  until,  at  length,  the  stock  of  momentum 
conferred  upon  it  by  the  man's  thrust  will  be  com- 
pletely exhausted  in  working  against  the  boy,  and  the 
boat,  after  a  momentary  rest,  will  resume  its  , onward 
course.  The  distance  to  which  the  boat  will  be  pro- 
pelled backwards  will  evidently  depend  upon  the 
amount  of  muscular  power  which  the  man,  as  it  were, 
suddenly  capitalizes  in  the  boat,  and  which  the  boat 
then  slowly  pays  out. 

We  call  people  who  possess  much  muscular  or 
other  power  energetic  ;  and  we  estimate  their  energy 
by  the  obstacles  they  overcome,  or,  in  other  words, 
by  the  work  they  do.  In  the  present  illustration 
the  man?s  energy  would  be  measured  by  the  distance 
to  which  the  boat  was  propelled  before  it  stopped,  r 

It  is  easy  to  transfer  this  conception  of  energy,  as 
the  power  of  doing  work,  to  inanimate  things;  and 
thus,  when  a  body  in  motion  overcomes  any  kind  of 
obstacles  in  .its  way,  parting  with  its  momentum  and 
more  or  less  coming  to  rest  in  the  process,  we  say  that 
it  has  energy  and  that  it  does  work. 

The  energy  of  moving  water  is  thus  measured  by 
the  intensity  of  the  opposing  forces  which  it  can 
overcome  multiplied  into  the  distance  which  ^  it  can 
travel  before  that  energy  is  exhausted;  that  is  to  say, 
by  the  work  it  does  before  it  is  itself  reduced  to  a  state 
of  rest.  In  the  case  under  consideration,  the  energy 
by  which  gravity  is  overcome,  for  a  greater  or  less  time, 
depends  upon  the  velocity  of  the  stream  ;  and  this  again 
depends  upon  the  height  of  the  water  in  the  vat 


46  SCIENCE  PRIMERS.  [MATERIAL 

above  the  tap.  Just  as  the  energy  of  the  horizontal 
stream  diminished  as  the  level  of  the  water  became 
lower,  so  d  jes  the  energy  of  the  vertical  stream 
diminish.  Hence,  as  the  vat  empties,  the  jet  be- 
comes shorter  and  shorter,  until  at  last  it  sinks  down 
to  nothing. 

The  energy  of  moving  water  makes  it,  under  some 
circumstances,  one  of  the  most  destructive  of  natural 
agents  ;  and,  under  others,  one  of  the  most  useful 
servants  of  man.  A  stream  is  water  falling  down  hill 
with  a  velocity  depending  upon  the  inclination  of  its  bed. 
As  it  falls  it  acquires  momentum  and,  hence,  energy; 
and  thus  a  mountain  stream,  suddenly  swollen  by  rain 
or  melting  snow,  will  tear  away  masses  of  rock  and 
sweep  everything  before  it'.  Nothing  can  look  softer  or 
more  harmless  than  a  calm  sea,  but  if  the  wind  sweep- 
ing over  its  surface  puts  the  water  in  motion,  it  strikes 
upon  the  shore  with  terrific  force  ;  and  its  energy  is  ex- 
pended in  throwing  up  great  waves,  which  lift  vast 
blocks  or  drive  masses  of  shingle  up  the  beach. 

In  all  kinds  of  watermills  it  is  the  energy  of  more 
or  less  rapidly  falling  water  which  is  turned  to  account. 
The  water  is  made  to  flow  against  buckets  or  floats 
attached  to  the  circumference  of  a  wheel.  Each  bucket 
or  float  is  therefore  an  obstacle  to  which  the  water 
transfers  some  of  its  own  motion ;  it  moves  away  and 
thus  makes  the  wheel  to  which  it  is  fastened  turn. 
But  the  turning  of  the  wheel  brings  a  new  obstacle  in 
the  way  of  the  stream.  This  is  treated  in  the  same 
fashion,  and  the  wheel  turns  still  further,  thus  intro- 
ducing another  obstacle  in  the  way  of  the  stream  upon 
which  the  same  effect  is  produced.  Thus  each  float, 
or  bucket,  is  a  means  by  which  some  of  the  momentum 


OBJECTS.]  INTRODUCTORY.  47 

of  the  stream  is,  as  it  were,  caught  and  transferred  to 
the  water-wheel,  which  consequently  turns  round  with 
a  certain  velocity. 

But  this  water-wheel  is  now  a  mass  of  matter  in 
motion,  and  therefore  itself  contains  a  store  of  energy 
or  power  of  doing  work.  If  a  cord  with  a  weight 
at  the  end  of  it  were  fastened  to  the  axle  of  the 
wheel,  the  cord  would  be  wound  upon  the  axle,  and 
the  weight  could  be  raised,  or,  in  other  words,  so 
much  work  would  be  done  by  the  turning  of  the 
wheel ;  and  we  should  thus  have  a  rough  measure  of 
the  amount  of  energy  which  had  been  given  up  by  the 
stream  to  the  wheel. 

The  machinery  of  the  mill  is  simply  a  set  of  con- 
trivances for  transferring  the  energy  stored  up  in  the 
water-wheel  to  the  place  in  which  work  has  to  be 
done.  In  a  flour-mill,  for  example,  a  series  of  wheels 
carries  it  from  the  water- wheel  to  the  grindstones,  which 
it  sets  in  motion. 

30.  The  Properties  of  Water  are  Constant. 

If,  whenever  there  is  a  shower,  you  catch  some  rain- 
water, you  will  find  that  it  possesses  all  the  properties 
which  have  been  described.  It  will  be  found  to  be 
an  almost  incompressible  liquid,  an  imperial  pint  of 
which  weighs  about  a  pound  and  a  quarter.  It  would 
make  no  difference  if  the  rain-water  were  collected  in 
Africa  or  in  New  Zealand  ;  or  if  it  had  been  obtained 
centuries  ago  and  kept  bottled  up  ever  since.  And 
there  is  every  reason  to  believe  that  rain-water  will 
have  exactly  the  same  properties  a  hundred  or  a 
thousand  years  hence.  So  far  as  the  properties  of 
5 


48  SCIENCE  PRIMERS.  [MATERIAL 

rain-water  are  concerned  the   order  of  nature  is 
constant. 

This  however  is  by  no  means  the  same  thing  as 
saying  that  the  properties  of  water  are  always  the 
same.  In  fact  the  properties  of  the  substance,  water, 
vary  immensely  according  to  the  conditions  to  which 
it  is  exposed  ;  but,  under  the  same  conditions,  they  are 
the  same,  so  that  we  may  still  say  that,  so  far  as 
water  is  concerned,  the  order  of  nature  is  constant. 

31.  Increase  of  Heat  at  first  causes  Water 
to  Increase  in  Volume. 

It  has  been  seen  that  a  certain  weight  cf  water 
always  has  the  same  volume  under  the  same  con- 
ditions. The  most  important  of  these  conditions  is 
the  heat  or  cold  to  which  it  is  exposed.  Water  which 
has  stood  for  some  time  in  a  warm  room  becomes  less 
in  volume,  or  contracts,  if  it  is  taken  into  a  cool 
place;  while  its  volume  increases,  or  it  expands,  if 
it  is  made  hot.  The  same  thing  is  true  of  quick- 
silver, of  spirit,  and  of  liquids  in  general.  A  thermo- 
meter is  simply  a  small  flask — -the  bulb — with  a  long 
and  narrow  neck — the  tube — filled  with  as  much  mer- 
cury or  spirit  as  will  rise  a  short  distance  into  the  neck. 
If  the  liquid  in  the  bulb  is  warmed,  its  volume  is  in- 
creased and  it  overflows  into  the  tube,  increasing  the 
height  of  the  column  of  liquid  in  the  tube.  If,  on 
the  other  hand,  the  liquid  in  the  bulb  is  cooled,  its 
volume  is  diminished  ;  and,  as  it  shrinks,  the  column 
of  liquid  in  the  tube  flows  back  into  the  bulb,  and 
the  level  of  the  top  of  the  column  is  lowered. 

If  a  mark  is  made  on  the  tube,  or  on  a  scale  fixed 
to  it,  at  the  point  which  the  liquid  reaches  when  the 


OBJECTS.]  INTRODUCTORY.  49 

bulb  is  placed  in  boiling  water ;  and  another  mark 
at  the  point  to  which  it  sinks  when  the  bulb  is  in 
melting  ice  ;  and  the  space  between  the  two  marks  is 
divided  into  180  equal  parts',  each  of  these  parts  is 
what  is  called  a  "degree" in  the  thermometers  ordinarily 
used  in  this  country  (called  Fahrenheits).  And  if 
the  boiling-point  is  counted  as  212°  the  freezing-point 
must  be  32°  (212—32  =  180).  With  the  same  amount 
of  heat  the  fluid  in  the  tube  always  stands  at  the  same 
degree,  and  hence  the  instrument  measures  tem- 
perature. 

That  hot  water  is  lighter  than  cold  is  easily  seen 
when  a  bath  is  filled  from  two  taps,  one  of  hot  and 
one  of  cold  water,  which  run  at  the  same  time.  Un- 
less care  is  taken  to  stir  the  water,  the  top  of  the  bath 
will  be  very  much  hotter  than  the  bottom.  Thus,  an 
imperial  pint  of  water  weighs  a  pound  and  a  quarter 
only  at  a  certain  temperature  or  degree  of  warmth, 
namely  at  62° ;  if  it  is  made  hotter  its  volume  increases, 
and  therefore  its  specific  gravity  diminishes. 

It  was  for  this  reason  that  in  §  22  the  weight  of  the 
same  volume  of  water  was  said  to  be  constant  under 
the  same  conditions;  and,  of  course,  the  same 
qualification  must  be  borne  in  mind  when  we  speak 
of  the  weight  of  a  cubic  inch  of  water  being  about 
252  and  a  half  grains.  Its  weight  is  in  fact  252-45 
grains  only  when  Fahrenheit's  thermometer  stands  at 
62° — but  as  this  is  the  temperature  of  ordinary  mild 
weather,  and  the  expansion  or  contraction  of  water 
for  a  degree  about  this  temperature  amounts  to  less 
than  3-oV(Ttn  of  its  volume,  the  weight  of  a  cubic  inch 
may  for  all  practical  purposes  be  taken  as  252  and  a 
half  grains. 


50  SCIENCE  PRIMERS.  [MATERIAL 

32.  Increase  of  Heat  at  length  causes 
Water  to  become  Steam. 

Thus  a  change  is  effected  in  the  properties  of  water 
by  heating  it  ever  so  little.  If  it  is  more  strongly 
heated  a  still  greater  change  takes  place.  You 
know  what  happens  when  a  saucepan  containing 
water  is  put  on  the  fire.  The  water  gets  hotter  and 
hotter,  then  it  begins  to  simmer,  and  finally,  when 
it  reaches  212°,  it  boils  away  into  steam,  which  passes 
into  the  air  and  disappears.  .  If  the  boiling  is  carried 
on  long  enough  all  the  water  vanishes.  It  looks  at 
first  as  if  the  water  had  been  destroyed  by  the  heat. 
In  reality,  however,  not  a  particle  of  water  has  been 
destroyed.  It  has  merely  changed  its  state.  The 
heat  has  altered  it  from  the  state  of  liquid  water  into 
that  of  gaseous  water,  vapour  or  steam. 

Try  the  same  experiment  with  a  tea-kettle  instead 
of  a  saucepan,  but  only  put  a  little  water  in  the  tea- 
kettle, and  shut  the  lid  well  down.  Then,  as  soon  as 
the  water  begins  to  boil,  the  steam  will  shoot  out  of 
the  spout  in  a  jet ;  and  this  will  go  on  as  long  as  any 
water  remains  in  the  kettle. 

The  steam,  as.  it  comes  out  of  the  spout,  is  so  hot 
that  it  will  scald  you  if  you  put  your  finger  in  it.  But 
you  may  satisfy  yourself  that  it  is  very  hot,  without 
scalding  your  fingers,  by  holding  a  stick  of  sealing-wax 
in  it.  The  wax  will  soften,  just  as  if  you  held  it  before 
the  fire.  Moreover,  if  you  look  through  the  steam,  just 
where  it  leaves  the  spout,  you  will  see  that  it  is  quite 
transparent ;  it  is  only  at  some  little  distance  from 
the  spout  that  it  loses  its  transparency,  changes  into 
a  white  opaque  cloud,  and  rapidly  vanishes  in  the  air. 


OBJECTS.]  INTRODUCTORY.  51 

33.  The  taking  away  of  Heat  from  Steam 
causes  the  Steam  to  change  into  Hot  Water. 

Now  take  a  cold  spoon,  or  a  cold  plate,  and  hold  it 
against  the  jet  of  steam,  for  a  moment  or  two. 
When  you  take  it  away,  you  will  find  that  it  is  quite  wet, 
being  covered  with  drops  of  warm  water,  and,  more- 
over, the  cold  spoon,  or  plate,  has  become  warm. 
And  if  you  fit  a  long  cold  metal  pipe  to  the  nozzle 
of  the  tea-kettle,  you  will  find  that  no  steam  at  all 
issues  from  the  end  of  the  pipe,  but  only  water,  while 
the  pipe  becomes  warmed. 

Thus  the  heat  passes  from  the  fire  into  the  sauce- 
pan, or  kettle,  and  thence  to  the  water  which  they 
contain  ;  the  water  gets  hotter  and  hotter,  and,  when 
it  has  taken  in  a  certain  quantity  of  heat,  it  becomes 
steam,  or  vapour  of  water.  When  the  steam  comes 
against  the  cold  plate,  or  passes  through  the  cold 
pipe,  it  gives  up  the  heat  it  has  taken  in  to  the  plate, 
or  the  metal  of  the  pipe.  They  carry  off  the  heat 
which  kept  the  water  in  the  condition  of  a  vapour, 
and  so  it  passes  bacK into  the  condition  of  liquid. 

Thus  steam  and  water  are  two  conditions  of  the 
same  thing,  water;  they  are  effects  of  the  quantity 
of  heat  which  the  water  has  taken  in. 

34.  When  Water  is  changed  into  Steam, 
its  Volume  becomes  about  1,700  times  greater 
than  it  was  at  first. 

If  you  could  measure  and  weigh  the  water  in  your 
kettle  to  begin  with,  and  then  measure  and  weigh  all 
the  steam  into  which  the  heat  of  the  fire  changes  it, 
you  would  find  that  the  bulk  of  the  steam  was  nearly 
1,700  times  as  great  as  the  bulk  of  the  water,  though 


52  SCIENCE  PRIMERS.  [MATERIAL 

the  weight  of  the  steam  would  be  exactly  the  same 
as  that  of  the  water.  If  you  had  a  small  square  cup 
like  a  die,  the  inside  measure  of  which  was  exactly 
one  inch  each  way,  it  would  hold  one  cubic  inch  of 
water.  If  this  cup  full  of  water  were  heated  till  all 
the  water  was  turned  into  steam,  the  steam  would 
nearly  occupy  a  cubic  foot,  since  there  are  1,728 
cubic  inches  in  a  cubic  foot  A  cubic  inch  of  water 
weighs  252!  grains,  and  the  steam  into  which  it  is 
converted  has  just  the  same  weight.  Thus  we  may 
say  that  steam  is  water  expanded  by  heat  into  a 
vapour  which  is  of  1,700  times  less  specific  gravity  than 
water.  On  the  other  hand,  a  pint  of  steam  allowed 
to  cool,  becomes  converted  into  a  quantity  of  water, 
which  measures  only  TTVrrth  of  a  pint,  though  it  weighs 
just  as  much  as  the  whole  pint  of  steam  did.  The 
steam,  therefore,  is  condensed  to  a  TTVo*h  of  its 
volume  of  water. 

The  power  with  which  water  expands  when  it  is 
converted  into  steam  is  very  great.  If  you  were  to 
stop  up  the  nozzle  of  the  tea-kettle,  the  steam,  inside 
the  kettle,  in  trying  to  expand,  would  burst  open  the 
lid ;  and  if  you  were  to  fasten  down  the  lid,  it  would 
pretty  soon  burst  the  kettle  itself.  You  sometimes 
hear  of  the  strong  boilers  of  steam-engines  being 
burst  in  this  way. 

35.  Gases  or  Elastic  Fluids.     Air. 

Here  is  a  glass  flask  with  a  long  neck  and  an  open 
mouth.  If  we  pour  water  in  at  the  mouth  until  it 
rises  to  the  lip  we  say  that  the  flask  is  full  of  water. 
If  we  now  pour  the  water  out  we  say  that  the  flask  is 
empty.  But  is  it  empty?  Press  the  flask  mouth 


OBJECTS.]  INTRODUCTORY.  g^      53 


downwards  into  a  glass  jar  full  of  water.  If  the  flask 
were  empty  there  would  be  no  reason  why  the  water 
should  not  enter  the  neck  of  the  flask  and  stand  at 
the  same  height  inside  the  neck  as  it  does  outside. 
If  you  take  an  "  empty  "  glass  tube  open  at  each  end 
and  press  it  down  into  the  water,  the  water  inside  and 
the  water  outside  will  stand  at  the  same  level.  But  if 
you  put  your  finger  on  the  upper  end  of  the  tube  so 
as  to  convert  it  into  a  closed  vessel,  the  water  will 
enter  the  lower  end  only  a  little  way.  So  with  the 
flask,  the  water  enters  the  neck  only  a  little  way. 
Hence  there  is  something  inside  the  "  empty  "  tube 
and  in  the  "empty"  flask;  something  which  is  mate- 
rial, because  it  occupies  space  and  offers  resistance. 
In  fact  the  flask  is  full  of  that  form  of  matter  which 
is  termed  air,  a  thick  coat  of  which  surrounds  the 
earth  as  the  atmosphere.  Air  has  weight,  as  you 
will  learn  more  fully  by  and  by;  and  that  air  in 
motion  can  transfer  that  motion  to  other  bodies  you 
are  taught  by  the  effects  of  the  winds,  which  are 
merely  air  in  motion. 

Air  therefore  has  all  the  characters  of  a  material 
substance.  Moreover  it  is  a  fluid,  for  it  fits  itself 
exactly  to  the  shape  of  any  vessel  which  contains  it ; 
its  parts  are  very  easily  moved,  or  we  should  feel  its 
resistance  every  time  we  move  a  limb ;  that  it  "flows  " 
is  seen  in  every  breeze  and  every  time  you  use  a  pair 
of  bellows,  when  the  air  is  driven  in  a  stream  out  of 
the  nozzle ;  and  it  presses  on  all  sides  anything 
contained  in  it. 

But  though  air  is  a  fluid  it  is  not  a  liquid.  In  the 
first  place  it  is  very  compressible.  We  saw  that  the 
water  entered  a  little  way  into  the  tube  or  the  neck  of 


54  SCIENCE  PRIMERS.  [MATERIAL 

the  flask  in  the  preceding  experiment.  The  reason 
of  this  is  that  the  water  compresses  the  air  into  a 
smaller  volume.  A  bag  full  of  air,  such  as  a  common 
air-cushion,  can  be  squeezed  till  the  air  in  its  interior 
occupies  a  much  smaller  volume ;  and,  if  you  treat  a 
syringe  full  of  air  in  the  same  way  as  the  syringe  full 
of  water  was  treated,  you  will  find,  if  the  piston  fits 
well,  that  it  can  be  driven  down  some  distance  and 
then  springs  back  again.  Air  in  fact  is  not  only  a 
compressible,  but  it  is  an  elastic  fluid  or  gas.  Heat 
expands  air  just  as  it  expands  water,  but  the  expansion 
of  air  for  the  same  degree  of  heat  is  much  greater. 


36.  Steam  is  an  Elastic  Fluid  or  Gas. 

In  all  the  properties  which  have  been  mentioned 
water  in  the  form  of  steam  is  an  elastic  fluid  or  gas 
like  air. 

If  a  little  water  is  placed  in  the  flask  mentioned 
in  the  preceding  section  all  the  "  empty  "  part  of  the 
space  will  contain  air.  If  the  flask  is  now  made  hot 
the  water  will  at  length  boil,  bubbles  of  steam  forming 
in  the  water  and  breaking  at  its  surface.  By  degrees, 
the  air,  which  at  first  lay  above  the  water,  will  be 
driven  out ;  and,  if  the  whole  flask  is  kept  hot,  the 
"empty"  part  of  it  will  be  full  of  the  gaseous  water, 
which  is .  transparent  and  colourless  like  air.  The 
steam  flows  out  of  the  mouth  of  the  flask  still  a  clear 
and  colourless  gas;  but  it  soon  cools  and  becomes 
condensed  as  a  cloud  of  small  particles  of  fluid  water. 

Steam  is  lighter  than  air,  and  hence  it  rises  in  the 
air,  just  as  bodies  which  are  lighter  than  water  rise 
in  water. 


OBJECTS.]  INTRODUCTORY.  55 

37.  Gases  and  Vapours. 

Air  is  as  much  a  gas  in  the  coldest  winter  as  it  is  in 
the  hottest  summer.  But  air  can  be  liquefied  by  ex- 
posing it  to  a  very  low  temperature,  while,  at  the  same 
time,  it  is  subjected  to  an  extremely  great  pressure. 
Thus,  the  difference  between  gases  like  air,  which  are 
condensed  wiih  extreme  difficulty,  and  gases  like 
steam,  which  are  condensed  easily,  is  only  one  of 
degree.  Nevertheless  there  is  a  certain  convenience 
in  distinguishing  those  gases,  which,  like  steam,  are 
easily  condensed  as  vapours.  In  what  we  ordinarily 
call  steam,  all  the  water  of  which  it  is  composed  re- 
mains gaseous  only  at  and  above  the  temperature  of 
boiling  water  (212°  Fahrenheit).  Cooled  ever  so 
little  below  this  point,  most  of  it  becomes  condensed 
into  hot  liquid  water.  However,  it  must  be  recol- 
lected that  though  that  particular  form  of  gaseous 
water  which  we  call  steam  exists  only  at  and  above 
the  temperature  of  boiling  water,  yet  water  is  capable 
of  existing  in  the  gaseous  state  down  to  the  freezing- 
point. 

Suppose  that  when  our  boiling  flask  contained 
nothing  but  water  and  steam,  the  mouth  were  stopped 
and  the  lamp  removed.  Then,  so  long  as  the  tem- 
perature of  the  whole  remained  at  that  of  boiling 
water,  every  cubic  inch  of  steam  above  the  water 
in  the  flask  would  weigh  about  *th  of  a  grain,  since 
100  cubic  inches  weigh  about  15  gra'ns.  Suppose  the 
capacity  of  the  flask,  exclusively  of  the  fluid  water 
in  it,  to  be  100  cubic  inches.  Then,  to  begin  with, 
the  gaseous  water  which  it  contains  will  weigh  15 
grains.  If  the  flask  is  now  allowed  to  cool,  more 
and  more  of  the  gaseous  water  condenses  into  the 


56  SCIENCE  PRIMERS.  [MATERIAL 


fluid  state ;  but,  even  down  to  the  freezing-point,  some 
water  will  remain  in  the  gaseous  state  and  will  fill  that 
part  of  the  flask  which  is  unoccupied  by  the  fluid  water. 
At  blood-heat  (98°)  the  gaseous  water  weighs  only 
about  a  grain,  though  it  still  occupies  100  cubic  inches; 
at  the  ordinary  temperature  of  the  air  it  weighs  not 
more  than  ^rd  of  a  grain  \  while,  at  the  freezing-point, 
its  weight  is  only  §-th  of  a  grain.  But  inasmuch  as 
there  is  less  and  less  actual  weight  of  water  in  the 
same  volume  of  gaseous  water  as  the  temperature 
falls,  it  follows  that  the  density,  or  specific  gravity,  of 
the  gaseous  water  must  be  less  the  lower  the  tem- 
perature. Moreover,  while,  at  the  boiling-point, 
gaseous  water  or  steam  resists  compression  with 
exactly  the  same  force  as  air  does,  the  lower  the 
temperature  the  more  easily  compressible  is  the 
gaseous  water. 

Suppose  an  elastic  bag  were  to  be  tied  on  to  the 
nozzle  of  a  kettle  full  of  boiling  water.  If  the  bag 
were  kept  as  hot  as  the  boiling  water  it  would  become 
fully  distended,  and  maintain  its  shape  in  spite  of 
the  pressure  of  the  air  upon  all  sides  of  it.  If  the  tag 
were  taken  away  it  would  retain  its  shape  so  long  as 
it  was  kept  as  hot  as  boiling  water ;  but,  if  it  were 
allowed  to  cool,  it  would  gradually  become  flattened 
by  the  outside  air  squeezing  up  the  less  and  less  resist- 
ing gaseous  water  of  the  lower  temperatures.  Hence, 
when  the  stopped  flask  has  been  allowed  to  cool,  the 
air  rushes  in  with  great  violence  if  it  is  opened. 

38.  The  Evaporation  of  Water  at  ordinary 
Temperatures. 

If  some   water   is   poured   into    a   saucer  and   is 


OBJECTS.]  INTRODUCTORY.  57 

allowed  to  stand  even  in  a  cool  room  or  in  the  open 
air,  you  know  that  it  sooner  or  later  disappears.  Wet 
clothes  hung  on  a  line  soon  dry — that  is  to  say,  the 
water  clinging  to  them  disappears  or  evaporates. 
The  disappearance  of  the  water  under  these  circum- 
stances results  from  the  property  just  mentioned.  In 
fact,  it  becomes  gaseous  water  of  the  density  appro- 
priate to  the  temperature,  and  as  such  mixes  with  the 
air  as  any  other  gas  would  do.  And  as  the  sea, 
lakes,  and  rivers,  are  constantly  giving  off  gaseous 
water  into  the  air  in  proportion  to  the  temperature, 
it  is  not  wonderful  that  the  atmosphere  always  contains 
gaseous  water. 

Air  is  said  to  be  moist  when  the  weight  oi  water  in 
a  given  quantity,  say  100  cubic  inches,  is  as  much,  or 
nearly  as  much,  as  can  exist  in  the  state  of  gas  at  the 
temperature.  Under  these  circumstances,  if  the  tem- 
perature is  lowered  even  a  very  little,  some  of  the 
gaseous  water  is  converted  into  liquid  water.  We 
see  this  in  hot  moist  weather,  when  the  outside  of  a 
tumbler  of  fresh  drawn  cold  spring  water  immediately 
becomes  bedewed.  The  gaseous  water  in  immediate 
contact  with  the  tumbler,  in  fact,  is  cooled  down  below 
the  point  at  which  it  can  all  exist  as  gas,  and  the 
superfluity  is  deposited  as  dew.  In  such  days  wet 
clothes  do  not  dry  well,  because  there  is,  already, 
nearly  as  much  gaseous  water  in  the  atmosphere  as 
the  amount  of  heat  marked  by  the  thermometer  can 
maintain  in  that  state. 

39.  When  Hot  Water    is    Cooled,  it  Con- 
tracts to  begin  with,  but  after  a  time  Expands. 
We  have  now  seen   what  a  wonderful  change   is 


58  SCIENCE  PRIMERS.  [MATERIAL 

brought  about  by  heating  water.  At  first,  it  ex- 
pands gradually  and  slightly  ;  but,  when  it  reaches  the 
boiling-point,  it  suddenly  expands  enormously,  and  is 
no  longer  a  liquid,  but  a  gas. 

On  the  other  hand,  if  warm  water  is  allowed  to 
cool,  it  gradually  contracts  till  it  reaches  the  ordinary 
temperature  of  the  air  in  mild  weather;  but,  if  the 
weather  is  very  cold,  or  if  the  water  is  cooled 
artificially,  it  goes  on  contracting  only  down  to  a 
certain  temperature  (39°),  and  then  begins  to  expand 
again.  In  this  peculiarity  water  is  unlike  all  other 
bodies  which  are  fluid  at  ordinary  temperatures. 
Hence  the  temperature  of  39°  is  that  at  which  pure 
water  has  its  greatest  density  or  specific  gravity,  and 
water  at  this  temperature  is  heavier,  bulk  for  bulk, 
than  the  same  water  at  any  ether  temperature.  There- 
fore if  water  at  the  top  of  a  vessel  is  cooled  down 
to  this  temperature,  it  falls  to  the  bottom,  and  if  the 
water  at  the  bottom  of  a  vessel  is  cooled  below  this 
temperature  it  rises  to  the  top. 

40.  Water  cooled  still  further  becomes  the 
transparent  brittle  solid  Ice. 

Our  tumbler  of  water,  if  put  out  of  doors  on  a  cold 
winter's  night,  would  gradually  cool  until  it  assumed  a 
temperature  of  39°  throughout.  Cooling  below  this 
temperature,  the  water  so  cooled  would  gradually 
accumulate  at  the  surface  by  reason  of  its  less  density, 
and  its  temperature  would  fall  till  the  thermometer 
placed  in  it  marked  32°.  As  soon  as  this  upper  water 
cooled  ever  so  little  below  32°,  a  film,  like  glass,  would 
form  on  its  surface  by  the  conversion  of  the  coldest 
fluid  water  into  solid  water,  or  ice.  And  if  all  the 


OBJECTS.]  INTRODUCTORY.  59 

water  cooled  down  to  the  same  degree  it  would  all 
gradually  change  into  the  same  kind  of  substance. 

In  this  condition  water  is  solid.  It  occupies  space, 
offers  resistance,  has  weight,  and  transmits  motion  as 
the  water  did,  but  if  you  shake  it  out  of  the  tumbler  in  a 
cold  place  it  retains  its  form  without  the  least  change. 
If  you  press  it,  it  proves  to  be  exceedingly  hard  and 
unyielding;  and,  if  the  pressure  is  increased,  it  be- 
comes crushed  and  breaks  like  glass.  It  may  thus  be 
crushed  to  powder,  and  the  ice  powder  can  be  formed 
into  heaps  as  if  it  were  sand. 

Just  as  any  quantity  of  steam  has  exactly  the  same 
weight  as  the  water  which  was  converted  into  it  by 
heat ;  so  the  ice  has  exactly  the  same  weight  as  the 
water  which  has  been  converted  into  it  by  taking  away 
heat. 

41.  Ice  has  less  Specific  Gravity  than  the 
Water  from  which  it  was  formed. 

But  though  the  ice  in  the  tumbler  has  the  same 
weight  as  the  water  had,  it  has  not  the  same  volume. 
The  expansion  which  began  at  39°  goes  on,  and  when 
water  passes  into  the  solid  state  its  volume  is  about 
^th  greater  than  it  was  at  39°.  Taking  water  at  this 
temperature  as  i.o,  ice  has  a  specific  gravity  of  0*916. 

But  although  water  in  freezing  expands  only  to  this 
small  amount,  it  resembles*  steam  in  the  tremendous 
force  with  which  it  expands.  If  you  nil  a  hollow 
iron  shell  quite  full  of  water,  screw  down  the  open- 
ing tight,  and  then  put  it  in  a  cold  place  where  the 
water  may  freeze,  the  water  as  it  freezes  will  burst 
the  iron  walls  of  the  shell.  You  know  that  when  the 
winter  is  severe,  the  pipes  by  which  water  is  brought 
6 


60  SCIENCE  PRIMERS.          '    [MATERIAL 

to  a  house  often  burst.  This  is  because  the  water  in 
them  freezes,  and,  being  unable  to  get  out  of  the 
pipe,  bursts  it,  just  as  you  may  burst  a  jacket  that  is 
too  tight  for  you  by  stretching  yourself.  Among  the 
bare  hill-tops,  or  on  the  face  of  cliffs  exposed  to  the 
weather,  the  strongest  and  hardest  rocks  are  every 
winter  split  and  broken,  just  as  if  quarryrcen  had 
been  at  work  at  them.  In  the  summer  the  rain- 
water gets  into  the  little  cracks  and  rifts  in  the 
stone  and  lodges  there.  Then  the  winter  comes 
with  its  cold  and  freezes  the  water.  And  the  water 
bursts  the  rocks  asunder  just  as  it  bursts  our  water- 
pipes. 

42.  Hoar  Frost  is  the  Gaseous  Water 
which  exists  in  the  Atmosphere,  condensed 
and  converted  into  Ice  Crystals. 

In  the  winter-time  you  often  notice,  on  a  clear 
sharp  night,  that  the  tops  of  the  houses  and  the 
trees  are  covered  with  a  white  powder  called  hoar 
frost ;  and,  on  the  windows  of  the  room  when  you 
wake  up,  you  see  most  beautiful  figures,  like  delicate 
plants.  Take  a  little  of  the  hoar-frost,  or  scrape 
off  some  of  the  stuff  that  makes  the  window  look 
like  ground  glass,  and  you  find  that  it  melts  in 
your  hand  and  turns  to  water.  It  is  in  fact  ice. 
And  if  you  look  at  the  figures  on  the  window  pane 
with  a  magnifying  glass  you  will  see  that  they  are 
made  up  bits  of  ice  which  have  a  definite  shape, 
and  are  arranged  in  a  regular  pattern.  Each  of  these 
definitely  shaped  bits  of  ice  has  been  formed  in  the 
following  way.  The  air  in  the  room  is  much  warmer 
than  that  outside,  and  there  is  mixed  with  it  nearly  as 


OBJECTS.]  INTRODUCTORY.  61 

much  water,  derived  from  the  breath  and  the  evapora- 
tion of  moist  surfaces,  as  can  maintain  itself  in  the 
gaseous  state  at  the  temperature.  The  window- 
panes,  being  thin,  are  cooled  by  the  outside  air, 
and  of  course  the  gaseous  water  inside  the  room, 
when  it  comes  in  contact  with  the  cold  window- 
panes,  becomes  condensed  on  them  into  fine  drops 
of  cold  water.  The  panes  becoming  colder  and 
colder,  these  minute  drops  at  last  freeze,  and  the 
water  not  only  becomes  solid,  but  it  crystallises ; 
that  is  to  say,  the  little  solid  masses  take  on  more  or 
less  regular  geometrical  forms  with  flat  faces,  inclined 
to  one  another  at  constant  angles,  so  that  they  re- 
semble bits  of  glass  cut  according  to  particular  fixed 
patterns.  All  ice  is  in  fact  crystalline,  but  in  ice 
which  has  been  formed  from  thick  sheets  of  water,  the 
crystals  are  so  packed  together  that  they  cannot  be 
distinguished  separately. 

43.  When  Ice  is  warmed  it  begins  to  change 
back  into  Water  as  soon  as  the  Temperature 
reaches  32°. 

A  lump  of  ice  brought  out  of  the  open  air  in  very 
cold  weather  may  have  a  temperature  of  30°,  or  20°,  or 
lower.  If  such  a  lump  is  brought  into  a  warm  room 
it  gradually  becomes  warmer,  but  remains  unchanged 
otherwise,  until  it  has  risen  to  32°.  Then  it  begins  to 
melt,  and  remains  at  32°  as  long  as  it  is  melting ;  and 
the  water  which  proceeds  from  it  is  at  first  also  at  32°. 

If  you  were  to  throw  a  lump  of  ice  into  the  middle 
of  a  hot  fire,  so  long  as  a  particle  of  ice  remained  as 
such,  it  would  have  a  temperature  of  32°  and  no  more. 
This  is  a  fact  exactly  parallel  to  that  which  is  observed 


62  SCIENCE  PRIMERS.  [MATERIAL 

when  water  is  raised  to  the  boiling-point.  So  long  as 
any  of  the  water  remains  unconverted  into  steam  it 
becomes  no  hotter.  Moreover  the  steam  itself  is  at 
first  at  212°. 

44.  Ice  the  solid,  Water  the  liquid,  and 
Steam  the  gas,  are  three  states  of  one  na- 
tural object ;  the  Condition  of  each  State 
being  a  certain  Amount  of  Heat. 

Ice,  liquid  water,  and  steam,  are  three  things  as 
unlike  as  any  three  things  can  well  be.  What  do  we 
mean  then  by  saying  that  they  are  states  of  one  sub- 
stance, water? 

What  we  really  mean  is  that  if  we  take  a  given 
quantity  of  water,  say  a  cubic  inch,  and  change  it 
first  into  ice  and  then  into  steam,  there  is  something 
which  remains  identically  the  same  through  all  these 
changes.  This  something  is,  in  the  first  place,  the 
weight  of  the  material  substance.  The  water  weighs 
2521  grains,  the  ice  into  which  it  is  converted  weighs 
25 2-g-  grains,  and  the  steam  produced  from  it  weighs 
25  2 \  grains.  In  the  second  place,  the  same  force 
would  cause  the  ice,  the  water,  and  the  steam,  to 
move  with  the  same  rapidity ;  and,  when  set  in  motion, 
they  would  produce  the  same  effect  upon  anything 
movable  against  which  they  struck, 

In  the  third  place,  when  you  study  chemistry, 
you  will  learn  that  the  ice.  the  steam,  and  the  liquid 
water,  would  yield  the  same  weight  of  the  same  two 
gases,  oxygen  and  hydrogen,  and  nothing  else. 
Every  one  cubic  inch  of  water,  1,700  cubic  inches  of 
steam,  and  i^  cubic  inch  of  ice,  yield  28^  grains  of 


OBJECTS.]  IN  TROD  UCTOR  Y.  63 

hydrogen,  with  224—$  grains  of  oxygen,  and  nothing 
else.     (See  §  50.) 

'As  there  is  not  the  slightest  difference  in  weight 
between  a  given  quantity  of  water  and  the  ice,  or  the 
steam,  into  which  it  may  be  converted,  it  is  clear  that 
the  heat  which  is  added  to  or  taken  from  the  water  to 
give  rise  to  these  several  states,  can  possess  no  weight. 
If  then  heat  is  a  material  body,  it  must  be  devoid 
of  weight — and  hence,  in  former  times,  heat  was 
called  an  imponderable  substance.  It  was  thought 
to  be  a  kind  of  fluid,  called  caloric,  which  had  no 
weight,  and  which  drove  the  particles  of  bodies 
asunder,  when  it  entered  them  as  they  were  heated, 
and  let  them  come  together  as  it  left  and  they  grew 
cool. 

45.  The  Phenomena  of  Heat  are  the 
Effects  of  a  rapid  Motion  of  the  Particles 
of  Matter. 

This  much,  however,  is  certain  :  that  heat  can  be 
caused  by  motion.  Every  boy  knows  that  a  metal  button 
may  be  made  quite  hot  by  rubbing  it.  A  skilful  smith 
will  hammer  a  piece  of  iron  red  hot.  The  axles  of 
wheels  become  red  hot  by  rubbing  against  their  bear- 
ings, if  they  are  not  properly  lubricated  ;  and  even  two 
pieces  of  ice  may  be  melted  by  the  heat  evolved  when 
they  are  rubbed  together.  And  there  are  abundant 
other  reasons,  as  you  will  find  when  you  study  physics, 
for  the  belief  that  the  sensation  we  call  heat,  and  all 
the  phenomena  which  we  ascribe  to  heat,  are  the  effects 
of  the  rapid  motion  of  matter. 

However,  a  quiescent  body  may  be  made  hot  with- 
out exhibiting  the  least  appearance  of  motion.  The 


64  SCIENCE  PRIMERS.  [MATERIAL 

surface  of  the  water  in  a  tumbler  at  100°  is  just  as  un- 
ruffled as  that  of  the  same  water  at  32°.  What,  then, 
is  meant  by  saying  that  heat  is  a  kind  of  motion,  and 
that  the  greater  the  heat  in  any  body  the  greater 
the  amount  of  motion  in  that  body  ? 

The  answer  to  this  question  is  that  the  motion  which 
causes  the  phenomena  of  heat,  is  not  a  visible  mo- 
tion of  the  whole  mass  of  the  hot  body,  but  a  motion 
of  the  individual  particles  of  which  it  is  composed. 
And  each  particle  moves,  not  straight  forward,  but 
backwards  and  forwards  in  the  same  space,  so  that  its 
motion  may  be  roughly  compared  to  that  of  a  pendu- 
lum, or  to  that  of  the  balance-wheel  of  a  watch.  It  is 
in  fact  a  sort  of  vibratory  movement ;  each  vibration 
taking  place  through  a  very  short  distance  and  with 
extreme  rapidity.  The  sensation  of  heat  is  caused  by 
the  vibratory  movements  of  the  particles  of  matter, 
just  as  sound  is  so  caused.  The  prongs  of  a  tuning- 
fork  which  has  been  struck,  certainly  vibrate,  for 
you  can  see  them  do  so  if  the  note  is  low.  Jf  you 
now  put  your  ear  at  one  end  of  a  long  piece  of  timber 
and  the  handle  of  the  vibrating  tuning-fork  is  placed 
upon  the  other  end,  the  vibratory  motion  of  the 
tuning-fork  will  be  communicated  to  the  particles 
of  the  wood  and  will  be  loudly  heard.  All  the  time 
the  sound  is  heard  the  particles  of  the  wood  are 
vibrating.  Nevertheless,  the  wood  as  a  whole  does 
not  move,  but  its  particles  swing  backwards  and  for- 
wards through  such  a  minute  space  that  their  motion 
is  imperceptible. 

But  what  are  these  particles  of  matter  which  by 
their  vibration  give  rise  to  the  phenomena  of  heat  ? 


OBJECTS.  ]  INTRO D  UCTOR  Y.  65 

46.  The  Structure  of  Water. 

We  have  seen  that  pure  water  is  perfectly  clear  and 
transparent.  The  naked  eye  can  discern  no  differ- 
ence between  one  part  and  another.  In  other  words, 
it  has  no  visible  texture  or  structure.  It  does  not 
follow  that  it  really  possesses  none,  however,  for  there 
are  many  things  which  seem  to  be  the  same  through- 
out, or  homogeneous,  which  yet  show  structure 
if  they  are  examined  with  a  magnifying  glass.  Thus 
the  surface  of  a  sheet  of  fine  white  paper  looks  per- 
fectly even  and  smooth  to  the  eye  ;  but  a  magnifying 
glass  of  no  great  power  will  show  the  minute  woody 
fibres  of  which  it  is  made  up  ;  while,  under  a  power- 
ful microscope,  the  paper  looks  like  a  coarse  matting. 

But  if  we  put  a  small  drop  of  water  on  a  slide,  such 
as  is  used  for  microscopic  objects,  and  cover  it  over 
with  a  thin  glass  so  as  to  spread  it  out  into  a  film, 
perhaps  not  more  than  yoinnj-th  of  an  inch  thick,  it 
may  be  examined  with  the  very  highest  magnifying 
powers  we  can  command,  and  yet  it  looks  as  com- 
pletely homogeneous  and  shows  as  little  evidence  of 
being  made  up  of  separate  parts  as  before.  However, 
this  is  still  no  proof  that  the  water  is  not  made  up  of 
little  parts,  or  particles,  distinctly  separated  from  one 
another.  It  may  merely  mean  that  the  particles  are 
so  extremely  small  that  they  cannot  be  distinguished 
even  by  microscopes  which  magnify  four  or  five 
thousand  diameters. 

It  is  certain  that  solid  bodies  may  b3  divided 
into  particles  so  minute  that  the  best  microscopes 
show  no  trace  of  them.  Common  gum-mastic  cannot 
be  dissolved  by  water,  but  it  readily  dissolves  in 
strong  spirit  or  alcohol,  and  mastic  varnish  is  an 


65  SCIENCE  PRIMERS.  [MATERIAL 

alcoholic  solution  of  gum-mastic.  If  you  add  water 
to  mastic  varnish,  the  alcohol  takes  away  the  water 
and  the  mastic  falls  out,  or  precipitates,  as  a  curdy 
solid  composed  of  very  visible  whitish  particles.  But 
if  a  drop  of  the  varnish  is  added  to  a  good  deal,  say 
half  a  pint,  of  water  and  well  stirred  at  the  same  time, 
the  mastic,  though  it  is  still  precipitated  as  a  solid,  is 
in  a  state  of  extremely  minute  division.  No  separate 
solid  particles  of  mastic  are  visible  to  the  naked  eye, 
but  the  water  assumes  a  faint  milky  tinge. 

This  milkiness  arises  from  the  presence  of  solid 
particles  of  mastic  diffused  through  the  water ;  and 
yet,  if  the  experiment  has  been  properly  managed,  a 
drop  of  the  fluid  may  be  spread  out  as  before  and 
examined  with  the  highest  magnifying  powers,  and 
nothing  can  be  seen  of  such  particles.  So  far  as 
vision  goes  it  might  be  a  drop  of  pure  water.  Now 
our  best  microscopes  are  able  to  show  us  anything 
solid  which  has  a  diameter  of  nrTFurnrtn  °^  an  mcn> 
quite  distinctly  ,  and  probably  solid  opaque  particles 
of  much  smaller  size  would  make  themselves  ap- 
parent as  a  turbidity  or  cloudiness.  The  particles  of 
mastic  must  be  therefore  so  much  smaller  than  this 
that  they  remain  invisible.  Hence  it  follows  that 
if  water  were  made  up  of  separate  particles,  or 
droplets,  ro-^u^uth  of  an  inch  in  diameter,  and  thus 
had  the  structure  of  a  mass  of  very  fine  shot,  no 
microscope  that  has  yet  been  constructed  would  enable 
us  to  see  even  a  trace  of  that  structure.  We  could 
not  obtain  any  direct  evidence  of  it. 


OBJECTS.]  INTRODUCTORY.  67 

47.  Suppositions  or  Hypotheses ;  their 
Uses  and  their  Value. 

When  our  means  of  observation  of  any  natural  fact 
fail  to  carry  us  beyond  a  certain  point,  it  is  perfectly 
legitimate,  and  often  extremely  useful,  to  make  a  sup- 
position as  to  what  we  should  see,  if  we  could  cairy 
direct  observation  a  step  further.  A  supposition  of 
this  kind  is  what  is  called  a  hypothesis,  and  the 
value  of  any  hypothesis  depends  upon  the  extent  to 
which  reasoning  upon  the  assumption  that  it  is  true, 
enables  us  to  explain  or  account  for  the  phenomena 
with  which  it  is  concerned. 

Thus,  if  a  person  is  standing  close  behind  you,  and 
you  suddenly  feel  a  blow  on  your  back,  you  have 
no  direct  evidence  of  the  cause  of  the  blow;  and 
if  you  two  were  alone,  you  could  not  possibly  obtain 
any;  but  you  immediately  suppose  that  this  person 
has  struck  you.  Now  that  is  a  hypothesis,  and  it  is 
a  legitimate  hypothesis,  first,  because  it  explains  the 
fact j  and  secondly,  because  no  other  explanation  is 
probable ;  probable  meaning  in  accordance  with  the 
ordinary  course  of  nature.  If  your  companion 
declared  that  you  fancied  you  felt  a  blow,  or  that 
some  invisible  spirit  struck  you,  you  would  probably 
decline  to  accept  his  explanation  of  the  fact.  You 
would  say  that  both  the  hypotheses  by  which  he 
professed  to  explain  the  phenomenon  were  extremely 
improbable  ;  or  in  other  words,  that  in  the  ordinary 
course  of  nature  fancies  of  this  kind  do  not  occur, 
nor  spirits  strike  blows.  In  fact,  his  hypotheses  would 
be  illegitimate,  and  yours  would  be  legitimate;  and, 
in  all  probaDility,  you  would  act  upon  your  own. 
In  daily  life,  nine-tenths  of  our  actions  are  based 


68  SCIENCE  PRIMERS.  [MATERIAL 

upon  suppositions  or  hypotheses,  and  our  success  or 
failure  in  practical  affairs  depends  upon  the  legitimacy 
of  these  hypotheses.  You  believe  a  man  on  the 
hypothesis  that  he  is  always  truthful;  you  give  him 
pecuniary  credit  on  the  hypothesis  that  he  is  solvent. 

Thus,  everybody  invents,  and,  indeed,  is  compelled 
to  invent,  hypotheses  in  order  to  account  for  phe- 
nomena of  the  cause  of  which  he  has  no  direct 
evidence  ;  and  they  are  just  as  legitimate  and  neces- 
sary in  science  as  in  common  life.  Only  the  scientific 
reasoner  must  be  careful  to  remember  that  which  is 
sometimes  forgotten  in  daily  life,  that  a  hypothesis 
must  be  regarded  as  a  means  and  not  as  an  end  ;  that 
we  may  cherish  it  so  long  as  it  helps  us  to  explain  the 
order  of  nature  ;  but  that  we  are  bound  to  throw  it 
away  without  hesitation  as  soon  as  it  is  shown  to  be 
inconsistent  with  any  part  of  that  order. 

48.  The  Hypothesis  that  Water  is  com- 
posed of  Separate  Particles  (Molecules), 

It  has  been  pointed  out  that  we  cannot  see,  and 
indeed  that  there  is  not  much  hope  of  our  ever  being 
able  to  see,  the  separate  particles  of  water,  even  if  water 
is  composed  of  such  particles.  But  it  is  perfectly 
legitimate  to  suppose  that  water  is  made  up  of  such 
particles,  if  that  hypothesis  will  enable  us  to  explain 
the  properties  of  water. 

Let  us  suppose  then  that  any  portion  of  fluid  water  is 
really  composed  of  a  prodigious  number  of  particles  less 
(and  probably  much  less)  than  a  millionth  of  an  inch 
in  diameter.  We  may  call  these  particles  molecules.1 

1  Diminutive  of  moles,  a  mass. 


OBJECTS.]  1NTROD  UCTOR  Y.  69 

We  are  justified,  in  accordance  with  the  general 
properties  of  matter  (§  18),  in  supposing  that  these 
molecules  tend  to  approach  one  another.  But  the 
fact  that  water  is  slightly  compressible  justifies  the 
supposition  that  its  molecules  are  not  in  actual  con- 
tact,  but  that  they  are  separated  by  interspaces,  just  as 
the  motes  in  the  air  of  a  dusty  room  are  so  separated.  ' 

What  is  it  that  keeps  the  molecules  apart?  We  have 
seen  that  great  mechanical  pressure  brings  them  but 
slightly  nearer  to  one  another ;  hence  there  is  an 
equivalent  resistance  of  some  kind  which  keeps  them 
apart.  This  resistance  must  have  the  same  origin  as 
the  sensation  which  we  know  as  heat,  for  it  has  been 
seen  that  diminution  of  heat  diminishes  the  bulk 
of  water ;  that  is,  allows  the  molecules  to  come  closer 
together ;  that  is,  diminishes  their  tendency  to  keep 
asunder.  Increase  of  heat,  on  the  other  hand,  in- 
creases the  volume  of  water ;  that  is  to  say,  drives  the 
molecules  further  apart,  or  increases  their  tendency 
to  keep  asunder. 

Suppose  we  call  the  cause  of  the  tendency  of  the 
molecules  of  water  to  come  together  an  attractive 
force  ;  and  the  cause  of  their  keeping  apart,  which 
manifests  itself  to  us  as  the  sensation  of  heat  and  is, 
as  we  have  seen,  in  all  probability,  a  rapid  vibratory  or 
whirling  motion  of  the  molecules,  a  repulsive  force  ; 
then,  in  the  liquid  state,  these  forces  are  so  adjusted 
that  the  molecules  are  quite  free  to  move,  and  yet 
hold  together. 

By  adding  heat  the  repulsive  force  is  increased, 
until  the  molecules  are  about  twelve  times  fas  ar  apart 
as  they  were  in  each  direction  ;  while  the  attractive 


70  SCIENCE  PRIMERS.  [MATERIAL 

force  is  overcome,  and  the  molecules  fly  off  in  all 
directions  as  soon  as  they  are  unconfmed.  On  the 
other  hand,  by  taking  heat  away,  the  repulsive  force 
is  diminished,  until  the  molecules  become  inseparable 
and  the  water  assumes  the  solid  form. 

It  is  probable  that  the  expansion  of  fluid  water,  at  a 
temperature  below  39°,  depends  upon  the  molecules 
taking  up  a  peculiar  arrangement  as  they  approach 
one  another.  If  sixteen  men  are  formed  into  a 
column,  four  deep,  and  each  man  a  foot  from  the 
other,  the  same  men  may  stand  closer  together  and 
yet  form  a  hollow  square,  which  occupies  a  larger  space. 
That  the  molecules  of  water  do  take  up  a  particular 
order  in  assuming  the  solid  condition,  is  shown  by 
the  crystalline  form  of  ice.  Each  crystal  of  hoar- 
frost owes  its  shape  to  the  arrangement  of  its  mole- 
cules, according  to  a  definite  geometrical  pattern. 

Thus  the  hypothesis  that  water  is  composed  of 
separate  molecules,  is  useful,  for  it  helps  us  to  some 
extent  to  explain  the  properties  of  water.  And,  when 
you  study  physics  and  learn  the  laws  of  motion,  you 
will  find  that  there  is  no  end  to  the  number  of  the 
truths  established  by  observation  and  experiment, 
which  can  be  explained  by  this  hypothesis.  Hence 
it  may  fairly  be  adopted  and  employed  as  a  means 
of  picturing  to  ourselves  the  order  of  nature,  so  long 
as  no  facts  are  discovered  which  are  inconsistent 
with  it. 

49.  All  Matter  is  probably  made  up  either 
of  Molecules  or  of  Atoms. 

The  same  reasons  which  lead  to  the  adoption  of 
the  hypothesis  that  water  is  composed  of  separate 


OBJECTS.]  INTRODUCTORY.  71 

particles  justify  its  extension  to  all  forms  of  matter 
whatever. 

The  metal  mercury  or  quicksilver,  for  instance, 
may  be  supposed  to  be  made  up  of  distinct  particles 
of  mercury  of  extreme  minuteness,  and  according  to 
the  temperature,  these  associate  themselves  in  the 
solid  (frozen  mercury),  liquid  (ordinary  quicksilver),  or 
gaseous  form  (vapour  of  mercury).  To  whatever  treat- 
ment pure  mercury  may  be  subjected,  we  cannot  get 
anything  but  mercury  out  of  it.  The  particles  of 
mercury  have  never  been  broken  up.  Hence  they  are 
generally  termed  atoms,  or  particles  that  cannot  be 
divided ;  and  mercury  is  said  to  be  an  element,  or 
a  substance  which  is  not  compounded  of  any  other 
substances. 

Here  is  a  case  in  which  it  is  very  useful  to  dis- 
tinguish between  fact  and  hypothesis.  The  matter  of 
fact  is  that,  up  to  the  present  time,  no  one  has  been 
able  to  get  out  of  pure  mercury  anything  but  pure 
mercury.  The  statement  that  mercury  is  a  simple 
substance,  and  therefore  never  can  be  broken  up  into 
any  other  substances,  is  a  hypothesis  which  future 
observation  and  experiment  may  or  may  not  confirm. 

A  hundred  and  fifty  years  ago  it  was  universally 
believed  that  water  was  as  much  an  element  as 
mercury.  But  water  is  now  well  known  to  be  a 
compound.  In  fact,  as  has  already  been  said,  the 
particles  of  water  may  be  very  readily  broken  up  or 
decomposed  (in  what  way,  you  will  learn  when 
you  study  chemistry)  into  two  totally  distinct  sub- 
stances, oxygen  and  hydrogen,  which  are  gaseous 
at  all  known  temperatures,  though  by  combining  vast 
pressure  with  extreme  cold  they  have  recently  been 
7  " 

1  s^fr^.  *^n\.  •**-  -*•»   *wT^a^ 


72  SCIENCE  PRIMERS.  [MATERIAL 

liquefied.  Each  of  these  gases,  according  to  our 
hypothesis,  consists  of  particles,  and  since  these  can 
by  no  known  means  be  further  broken  up,  they  are 
considered  to  be  atoms  like  those  of  mercury. 

Nine  parts  by  weight  of  pure  water  always  yield 
eight  of  oxygen  and  one  of  hydrogen.  The  hypo- 
thetical particle,  or  molecule  of  water,  therefore, 
must  be  composed  of  atoms  of  oxygen  and  hydrogen 
having  this  relative  weight ;  and  chemists  have  grounds 
for  believing  that  one  atom  of  oxygen  and  two 
atoms  of  hydrogen  exist  in  each  molecule  of  water. 
If  this  be  so,  the  structure  of  water  must  be  more 
complicated  than  we  thought  at  first ;  and  each 
particle  of  water  (the  molecule)  must  be  a  system 
composed  of  three  separate  atoms. 


50.  Elementary  Bodies  are  neither  de- 
stroyed nor  is  their  Quantity  increased  in 
N  ature. 

It  has  been  seen  that  when  a  cubic  inch  of  water 
is  dissipated,  by  heat,  it  is  not  destroyed,  but  that  it 
merely  changes  its  form  from  the  fluid  to  the  gaseous 
state,  while  its  weight  remains  unaltered.  If  the  same 
cubic  inch  of  water  is  decomposed  into  oxygen  and 
hydrogen  gases,  the  water  is  indeed  destroyed,  but 
the  matter  of  which  it  consisted  remains  unchanged 
in  weight.  If  the  water  weighed  252-5  grains,  the 
oxygen  gas  will  weigh  224/45  grains,  and  the  hydrogen 
gas  will  weigh  28*05  grains.  And  nothing  that  man 
has  been  able  to  do  has  affected  the  weight  of  a 
given  quantity  of  either  of  these  gases.  So  far  as  we 
know,  elementary  bodies  retain  their  weight  under  all 


OBJECTS.]  INTRODUCTORY.  73 

circumstances,  and  can  be  traced  by  it  whatever  shape 
they  may  take.  If  this  is  true  it  follows  that,  in  the 
order  of  nature,  matter  is  indestructible :  the 
quantity  of  it  neither  increases  nor  diminishes. 

Hence  it  follows  that  natural  things  and  artificial 
things  resemble  one  another  in  one  respect.  It  is 
true  of  both  that  the  matter  of  which  they  are  com- 
posed is  never  destroyed  and  never  increased ;  and 
therefore  the  order  of  events  in  nature  as  much 
consists  in  the  joining  together  and  putting  apart  of 
natural  bodies  by  natural  agencies,  as  the  order  of 
events  in  the  artificial  world  consists  in  the  joining 
together  and  the  putting  apart  of  natural  bodies  by 
human  agencies. 

51.  Simple  Mixture. 

In  order  to  learn  the  manner  in  which  water  may 
be  broken  up  into  its  elements  or  decomposed, 
you  must  turn  to  the  Primer  on  Chemistry.  But  as  a 
preliminary  to  the  study  of  that  science,  it  may  be 
useful  to  consider  some  simple  cases  of  composition 
and  decomposition  which  are  exemplified  by  water. 

If  half  a  pint  of  water,  coloured  by  putting  a  little 
ink  into  it,  is  added  to  the  same  quantity  of  clean 
water,  the  two  will  readily  mingle  ;  the  total  quantity  of 
water  will  be  a  pint ;  and  its  colour  will  be  just  half  as 
dark  as  that  of  the  coloured  half-pint.  This  is  a  case 
of  simple  mixture.  The  volume  of  the  mixture 
equals  the  sum  of  the  volumes  of  the  things  mixed, 
and  there  is  no  change  in  the  properties  of  these  things. 
So  when  water  evaporates,  the  gaseous  water  or 
vapour  mixes  with  the  air  in  the  same  way,  the  mole- 
cules of  the  one  body  dispersing  themselves  between 


74  SCIENCE  PRIMERS.  [MATERIAL 

the  molecules  of  the  other  until  there  is  the  same 
proportion  of  each  everywhere.  In  like  manner, 
sand  and  sugar  may  be  (and  unfortunately  often  are) 
mixed,  without  any  change  in  the  properties  of  either, 
or  in  the  space  which  they  primitively  occupied. 

On  the  other  hand,  oil  and  water  will  not  mix,  how- 
ever much  you  may  stir  the  two  together ;  and  the  oil, 
being  the  lighter,  rises  to  the  top  as  soon  as  the  fluid 
is  quiet.  Nor  will  quicksilver  and  water  mix,  but  the 
quicksilver,  being  very  much  heaviei  than  the  water, 
rushes  to  the  bottom  of  the  vessel  into  which  the  two 
are  put.  Neither  will  sand  nor  iron  filings  mix  with 
water ;  as  heavier  bodies,  they  also  sink  to  the  bottom. 
Nor  does  powdered  ice,  though  it  is  water  in  another 
shape,  mix  with  ice  cold  water ;  as  a  lighter  body,  it 
floats  at  the  top. 

52.  Mixture  followed  by  Increase  of  Den- 
sity ;  Alcohol  and  Water. 

Strong  spirit,  or  alcohol,  is  a  clear  transparent  fluid 
which  looks  like  water,  but  is  a  very  different  substance. 
For  example,  it  boils  at  a  much  lower  temperature,  it 
burns  with  a  blue  flame,  it  has  intoxicating  properties, 
and,  like  oil,  it  is  very  much  lighter  than  water.  Hence 
if  coloured  spirit  is  poured  gently  upon  the  surface  of 
water  the  spirit  rests  upon  the  water.  Suppose,  now, 
that  we  take  a  tall  measure  graduated  into  ten  equal 
parts.  Fill  the  lower  five  with  water,  and  then,  very 
gently,  pour  in  the  strongest  alcohol,  coloured  in 
some  way,  until  the  tenth  mark  is  reached.  We  shall 
have  five  volumes  of  water  below,  and  an  equal  quan- 
tity, or  five  volumes,  of  coloured  alcohol  above. 
Where  the  two  are  in  contact,  the  colour  will  be 


OBJECTS.]  INTRODUCTORY.  75 

diffused  into  the  water  for  a  short  distance,  but  not  far, 
showing  that  only  a  slight  mixture  is  taking  place. 
This,  however,  is  not  because  the  two  fluids  mingle 
with  difficulty  ;  for,  with  slight  stirring,  they  mix  com- 
pletely, and  you  have  a  fluid  the  colour  of  which  is 
about  half  as  intense  as  that  of  the  alcohol,  and  many 
of  the  other  properties  of  which  are  intermediate 
between  those  of  pure  alcohol  and  thoss  of  pure 
water. 

Thus  far,  nothing  further  than  simple  mixture,  as 
when  coloured  water  was  added  to  pure  water,  seems 
to  have  occurred ;  but,  in  reality,  something  more  has 
happened.  In  the  first  place,  the  mixture  is  a  good 
deal  warmer  than  either  of  its  components ;  that  is  to 
say,  heat  has  been  generated.  In  the  second 
place,  if  you  measure  the  volume  of  the  whole  fluid 
after  it  has  cooled,  it  no  longer  stands  at  the  mark 
ten  but  distinctly  lower,  or  about  nine  and  three- 
quarters.  As  the  volume  of  the  mixture  is  less 
than  the  sum  of  the  volumes  of  its  two  components, 
it  follows  that  the  density  of  the  mixture  must 
be  greater  than  a  density  midway  between  that 
of  the  water  and  that  of  the  alcohol.  In  other 
words,  the  molecules  in  the  mixture  do  not  occupy 
the  same  space  as  they  did  when  they  were  sepa- 
rate. The  result  is  the  same  as  if  the  ten  volumes 
had  been  compressed  until  they  occupied  only  nine 
and  three-quarters ;  so  that  the  effect  is  a  contraction 
similar  to  that  which  would  be  brought  about  by 
taking  away  heat  from  the  mixture.  In  fact,  as  we 
have  seen,  the  mixture  gives  out  a  quantity  of  heat. 

There  is  another  respect  in  which  the  mixture  is 
unlike  both  its  constituents.  It  both  boils  and 


76  SCIENCE  PRIMERS.  [MATERIAL 

freezes  at  a  much  lower  temperature  than  water 
does,  and  at  a  higher  temperature  than  alcohol  does. 
In  fact  pure  alcohol  has  not  yet  been  frozen.  If  the 
molecules  of  the  alcohol  were  merely  diffused  among 
those  of  the  water  as  water  is  diffused  through  wet 
sand,  they  ought  to  pass  into  the  gaseous  state  at  the 
same  temperature  as  that  at  which  alcohol  boils ;  and 
it  would  then  be  very  easy  to  separate  alcohol  from 
water  by  distillation.  But  the  fact  is  not  so;  alco- 
hol cannot  be  obtained  free  from  water  by  distillation 
unless  something  which  holds  water  very  strongly, 
such  as  quicklime,  is  added,  so  as  to  keep  all  the 
water  back  when  the  fluid  is  heated. 

Thus  alcohol  and  water,  mingled  together,  give  rise 
to  a  fluid  which  is  not  a  mere  mixture,  the  properties 
of  which  are  known  if  we  know  the  properties  of  its 
components ;  it  is,  in  strictness,  a  new  body,  in  which 
the  molecules  of  the  water  and  those  of  the  alcohol 
affect  one  another  to  a  certain  extent,  and  modify  the 
pre-existing  properties  of  each. 

This  effect  of  different  bodies  upon  one  another 
becomes  much  more  manifest  when  water  is  brought 
into  contact  with  certain  solids. 

53.  Solution  :  Water  Dissolves  Salt. 

If  a  spoonful  of  salt  is  put  into  a  tumbler  of  cold  water 
and  the  water  is  stirred,  the  salt  swiftly  vanishes  from 
view ;  and,  after  a  time,  so  far  as  our  sense  of  vision 
goes,  the  water  appears  to  be  just  what  it  was  before. 
But  if  the  water  in  the  tumbler  at  first  weighed  five 
ounces  and  the  salt  weighed  two  ounces,  the  water 
in  the  tumbler  will  now  weigh  seven  ounces;  the 
water  will  now  taste  salt,  the  salt  is  said  to  be 


OBJECTS.]  1NTROD  UCTOR  Y.  77 

dissolved,  and  the  solution  is  called  brine. 
Moreover,  the  solution  is  said  to  be  saturated,  for 
if  you  put  more  salt  in  it  will  remain  unchanged. 
Water,  in  fact,  will  dissolve  two-fifths  of  its  weight 
of  salt,  and  no  more.  If  the  brine  thus  formed  is  put 
into  a  wide  dish,  so  that  the  water  may  evaporate ;  or 
if  it  is  heated  and  the  water  boiled  away ;  as  fast  as  the 
water  diminishes,  a  quantity  of  salt,  equal  to  two-fifths 
of  the  water  which  is  converted  into  steam,  returns  to 
the  solid  state  and  falls  to  the  bottom  of  the  vessel. 
And  when  all  the  water  is  driven  off,  the  salt  which 
remains  will  have  exactly  the  weight,  and  all  the  other 
properties  which  it  had  before  it  was  dissolved  by  the 
water. 

Thus,  contact  with  water  has  had  a  very  singular 
effect  upon  the  salt.  It  appears  to  have  changed  one 
of  the  properties  of  the  salt,  namely,  its  solidity, 
but  to  have  left  all  the  rest  unaltered.  We  saw  just 
now  that  powdered  ice  does  not  mix  with  ice-cold 
water,  but  that  the  fragments  of  ice  remain  solid.  The 
moment,  however,  that  the  temperature  rises,  the 
cohesion,  or  sticking  together  of  the  molecules, 
which  is  the  characteristic  of  the  solid  state,  comes  to 
an  end ;  they  become  loose  and  free  to  move,  and  they 
mingle  with  the  surrounding  water.  Or  we  may  say 
that  the  ties  which  held  the  molecules  of  the  solid 
together  are  dissolved,  so  that  the  solid  water  becomes 
fluid. 

The  resemblance  of  this  process  to  the  dissolving 
of  salt  in  water  is  so  obvious  that,  in  common  lan- 
guage, it  is  often  said  that  a  lump  of  salt  or  of  sugar 
melts  away  in  water;  but  if  you  try  to  make  salt 
fluid  by  heat,  you  will  have  to  expose  it  to  a  very  high 


;S  SCIENCE  PRIMERS.  [MATERIAL 

temperature,  so  that  the  conversion  of  salt  from  the 
solid  state  into  the  liquid  state  by  solution  in  cold 
water  is  obviously  a  very  different  process  from  lique- 
faction by  heat.  Nevertheless  the  result  is  the  same 
so  far  as  the  condition  of  the  salt  is  concerned.  The 
cohesion  between  its  molecules  is  destroyed,  and  they 
distribute  themselves  evenly  among  the  molecules  of 
the  water,  just  as  the  molecules  of  steam  distribute 
themselves  among  the  molecules  of  air.  And,  when 
you  study  chemistry,  you  will  learn  how  it  may  be 
proved  that  the  smallest  drop  of  the  solution  of  salt 
contains  exactly  the  same  proportion  of  salt  as  the 
whole  does. 

If  brine  is  allowed  to  evaporate  slowly,  the  mole- 
cules of  the  salt  arrange  themselves,  as  the  water 
leaves  them,  in  beautifully  regular  cubical  crystals. 
You  may  see  them  form  easily  enough  if  you  watch  a 
drop  of  brine  gradually  dry  up  under  a  microscope. 
The  salt  crystals  contain  nothing  but  salt.  If  they 
are  heated  till  they  become  red-hot  they  pass  into  the 
fluid  state;  and  when  still  further  heated,  the  fluid 
salt  becomes  a  vapour  or  gas  and,  as  such,  flies  off 
into  the  air,  or  volatilizes. 

Thus  we  see  that  when  salt  and  water  are  brought 
into  contact,  the  salt  undergoes  a  certain  amount  of 
change,  while  the  water  does  not  remain  wholly  un- 
changed. For  brine  no  longer  boils  at  2 12°  but  re- 
quires a  considerably  higher  temperature.  The  salt,  as  it 
were,  holds  the  water  back  and  prevents  it  from  assum- 
ing the  gaseous  state  under  the  same  conditions  as  if  it 
were  pure,  just  as,  in  the  previous  case,  the  water  held 
the  alcohol  back ;  or  we  may  say  that  the  force  of  heat 
which  drives  the  molecules  of  liquid  water  apart,  when 


OBJECTS.]  INTRODUCTORY.  79 

steam  is  formed,  has  a  greater  resistance  to  overcome 
when  salt  is  dissolved  in  the  water.  And  just  as 
the  presence  of  alcohol  lowers  the  freezing  point  of 
the  water  with  which  it  is  mixed,  so  does  the  presence 
of  salt  lower  the  freezing  point  of  water.  Sea  water, 
which  is  a  weak  brine,  begins  to  freeze  at  about  27°; 
and  the  ice  which  is  formed  is  quite  pure,  while  the 
remainder  of  the  sea  water  becomes  richer  in  salt. 

If  we  mean  by  attraction  that  which  opposes  any 
force  which  tends  to  separate  bodies,  then  we  may  say 
that  the  molecules  of  salt  and  those  of  water  attract 
one  another.  And  such  attraction  between  molecules 
of  matter  of  different  kinds  is  called  chemical  at- 
traction. 

54.  Quicklime  and  Water  :  Plaster  of  Paris 
and  Water  :  Combination. 

Quicklime  is  a  substance  obtained  by  heating  chalk  or 
limestone  to  redness.  When  pure,  it  is  a  white  hard  solid 
which  can  be  made  to  pass  into  the  liquid  and  gaseous 
states  only  at  enormously  high  temperatures.  If  a 
lump  of  fresh  quicklime  is  placed  in  a  saucer  and  about 
one-third  of  its  weight  of  water  poured  upon  it,  there  will 
be  a  great  turmoil,  heat  will  be  evolved,  the  water  will 
disappear,  and  the  lime  will  crumble  down  into  a  soft 
white  powder.  This  operation  is  what  bricklayers  call 
slaking  lime.  And  if  no  more  water  has  been  added 
than  the  proportion  mentioned,  the  pure  white  powder 
which  results  will  be  solid  and  dry,  the  water  having 
to  all  appearance,  vanished. 

In  the  solution  of  salt  we  saw  a  solid  become 
fluid  under  the  influence  of  water ;  in  the  slaking  of 
lime  the  fluid  water  enters  into  the  structure  of  a  solid. 


So  SCIENCE  PRIMERS.  [MATERIAL 

If  more  water  is  added,  this  solid  dissolves  or  becomes 
liquid,  as  the  salt  did,  and  the  solution  is  called  lime- 
water.  By  carefully-managed  evaporation  of  the 
water  the  lime  may  be  recovered  in  the  form  of  crys- 
tals, just  as  the  salt  was  recovered.  But  there  is 
this  difference,  that  the  salt  crystals  contain  no  wa- 
ter, while  the  lime  crystals  not  only  contain  water, 
but  contain  exactly  the  same  proportion  as  exists 
in  slaked  lime,  that  is  to  say,  18  parts  water  to  56 
parts  lime. 

The  water  thus  bound  up  with  the  lime  into  a  new- 
solid  holds  on  so  firmly  to  the  lime  that  it  requires  a 
red  heat  to  separate  the  two.  The  lime  and  the  water 
are  said  to  be  chemically  combined ;  and  as  the 
proportion  of  lime  and  water  in  slaked  lime,  or  lime 
crystals,  is  always  the  same,  they  are  said  to  be  com- 
bined in  definite  proportions  ;  and  the  slaked  lime 
receives  the  special  name  of  hydrate  of  lime. 

Gypsum  or  Plaster  of  Paris  is  a  dry  white 
powder.  If  mixed  with  a  little  water  it  does  not  slake 
after  the  fashion  of  quick  lime,  but  the  mixture  soon 
sets  or  becomes  hard  ;  and,  at  the  same  time,  the 
greater  part  of  the  water  disappears.  In  fact,  it  has 
combined  with  the  plaster  of  Paris  and  forms  part  of 
another  hydrate,  in  which,  when  the  superfluous  mois- 
ture dries,  not  a  trace  of  water  is  to  be  seen.  It  is  this 
property  which  is  taken  advantage  of  when  plaster  of 
Paris  is  used  for  making  casts  and  moulds.  The  fluid 
plaster  is  poured  over  and  round  the  body  to  be  cast ; 
as  a  fluid,  it  applies  itself  conveniently  to  all  the  in- 
equalities of  its  surface  ;  and,  when  it  sets,  it  retains  the 
shape  which  it  has  thus  acquired.  Set  plaster  of  Paris 
may  be  perfectly  dry;  but  it  nevertheless  contains 


OBJECTS.]  INTRODUCTORY.  81 

between  \  and  \  of  its  weight  of  water,  fixed  and  form- 
ing an  integral  part  of  the  solid  hydrate.  And  if  the 
set  plaster  is  strongly  heated,  the  combined  water  is 
driven  off  and  it  returns  to  its  original  state. 

Gypsum  is  found  abundantly  in  nature,  in  the  shape 
of  beautiful  transparent  crystals  which  are  called 
selenite.  These  crystals  have  the  same  composition 
as  set  plaster,  that  is  to  say,  they  are  hydrates.  A 
thin  flake  of  such  a  crystal  viewed  with  the  highest 
powers  of  the  microscope  appears  perfectly  homo- 
geneous. Nevertheless,  there  is  good  reason  for  the 
conclusion  that  it  consists  of  molecules  of  water  and 
molecules  of  gypsum  which  hold  together  so  strongly 
that  they  form  a  hard  brittle  glassy  solid.  Moreover, 
the  molecules  of  the  hydrate  itself  hold  together  more 
strongly  in  some  directions  than  in  others.  It  is 
very  easy  to  split  the  crystals  lengthwise ;  while  much 
more  force  is  needed  to  cut  them  crosswise  and  then 
they  do  not  split,  but  break. 

Glauber's  salts  and  Epsom  salts  are  other  examples 
of  solids  which  dissolve  in  water  and  separate  in  the 
crystalline  form  as  the  water  evaporates ;  and  which, 
like  lime  and  gypsum,  combine  with  a  definite  pro- 
portion of  water  to  form  crystalline  compounds. 
In  fact,  each  of  these  glassy  brittle  solids  contains 
more  than  half  its  weight  of  water. 

Thus  we  see  that  two  bodies,  of  which  water  is  one, 
may  combine  together  to  give  rise  to  something  dif- 
ferent from  either.  And  we  are  thus  led  to  the  science 
of  chemistry,  which  tells  us  exactly  how  bodies 
combine,  what  comes  of  their  combination,  and 
how  compounds  may  be  separated,  into  their  con- 
stituents. 


82  SCIENCE  PRIMERS.  [MATERIAL 

55.  Mineral  bodies  may  take  on  definite 
shapes  and  grow,  or  increase  in  size,  by  the 
addition  of  like  parts. 

Water  and  all  the  other  natural  bodies  which  have 
hitherto  been  mentioned,  are  what  are  called  mineral 
bodies,  although,  in  common  use,  the  term  mineral 
is  usually  restricted  to  ores  and  metals.  Now  we  have 
repeatedly  had  occasion  to  remark  that,  under  certain 
circumstances,  not  only  water,  but  many  other  mineral 
bodies,  assume  regular  shapes.  The  most  familiar 
example  is  that  of  the  beautiful  imitation  of  leaves 
and  foliage  which  is  presented  by  the  ice  which  forms 
on  a  window  in  winter.  But  we  have  also  seen  that 
common  salt,  lime,  gypsum,  Glauber's  salts  and  Epsom 
salts,  also  assume  the  crystalline  form  as  they  or  their 
compounds  with  water,  are  deposited  from  their 
solutions.  And  if  a  drop  of  solution  of  Glauber's  salts 
or  of  Saltpetre,  is  allowed  to  evaporate  under  the 
microscope,  a  wonderful  spectacle  will  be  presented. 
As  the  salt  assumes  the  solid  state,  the  crystals 
suddenly  appear  in  the  field  of  view  as  needles  and 
plates  disposed  in  beautiful  patterns,  which  rival  those 
of  hoar  frost,  though  they  are  quite  different  from 
them.  In  fact,  as  you  will  learn  if  you  study 
crystallography,  every  crystallizable  substance  has 
its  proper  crystalline  forms  and  never  departs  from 
certain  strictly  related  geometrical  figures. 

A  crystal  of  any  of  these  substances  will  grow  if 
placed  under  proper  conditions.  Thus,  if  a  crystal  of 
common  salt  is  hung  by  a  thread  in  a  saturated 
solution  of  salt,  which  is  exposed  to  the  air,  so  as  to 
allow  the  water  to  evaporate  slowly,  the  molecules  of 
the  salt  which  is  left  behind  and  can  no  longer  be  held 


OBJECTS.]  INTRODUCTORY.  83 

in  solution,  deposit  themselves  on  the  crystal  in  regular 
order  and  increase  its  size  without  changing  its  form. 
And,  in  this  way,  the  small  crystal  may  grow 
to  a  great  size.  The  large  crystals  of  sugar  candy, 
which  consist  of  sugar  and  water  deposited  from  a 
strong  syrup  or  saturated  solution  of  sugar,  grow  in 
the  same  fashion,  upon  threads  suspended  in  the 
evaporating  syrup.  In  this  mode  of  growth  you  will 
observe  that  the  enlargement  is  effected  by  addition 
to  the  outside  of  the  growing  body ;  and  moreover  the 
matter  which  is  added,  namely,  the  salt  or  the  sugar, 
already  exists  as  salt  in  the  brine  or  as  sugar  in  the 
syrup. 

B.  LIVING   BODIES. 

56.  The  Wheat  Plant  and  the  substances 
of  which  it  is  composed. 

Every  one  has  seen  a  cornfield.  If  you  pluck  up 
one  of  the  innumerable  wheat  plants  which  are 
fixed  in  the  soil  of  the  field,  about  harvest  time,  you 
will  find  that  it  consists  of  a  stem  which  ends  in  a 
root  at  one  end  and  an  ear  at  the  other,  and  that 
blades  or  leaves  are  attached  to  the  sides  of  the 
stem.  The  ear  contains  a  multitude  of  oval  grains 
which  are  the  seeds  of  the  wheat  plant.  You  know 
that  when  these  seeds  are  cleared  from  the  husk  or 
bran  in  which  they  are  enveloped,  they  are  ground 
into  fine  powder  in  mills,  and  that  this  powder  is  the 
flour  of  which  bread  is  made.  If  a  handful  of  flour 
mixed  with  a  little  cold  water  is  tied  up  in  a  coarse 
cloth  bag,  and  the  bag  is  then  put  into  a  large  vessel 
8 


84  SCIENCE  PRIMERS.  [MATERIAL 

of  water  and  well  kneaded  with  the  hands,  it  will 
become  pasty,  while  the  water  will  become  white.  If 
this  water  is  poured  away  into  another  vessel,  and  the 
kneading  process  continued  with  some  fresh  water,  the 
same  thing  will  happen.  But  if  the  operation  is  re- 
peated the  paste  will  become  more  and  more  sticky, 
while  the  water  will  bo  rendered  less  and  less  white, 
and  at  last  will  remain  colourless.  The  sticky 
substance  which  is  thus  obtained  by  itself  is  called 
gluten ;  in  commerce  it  is  the  substance  known  as 
maccaroni. 

If  the  water  in  which  the  flour  has  thus  been 
washed  is  allowed  to  stand  for  a  few  hours,  a  white 
sediment  will  be  found  at  the  bottom  of  the  vessel, 
while  the  fluid  above  will  be  clear  and  may  be  poured 
off.  This  white  sediment  consists  of  minute  grains  of 
starch,  each  of  which,  examined  with  the  microscope, 
will  be  found  to  have  a  concentrically  laminated 
structure.  If  the  fluid  from  which  the  starch  was 
deposited  is  now  boiled  it  will  become  turbid,  just  as 
white  of  egg  diluted  with  water  does  when  it  is  boiled, 
and  eventually  a  ^hitish  lumpy  substance  will  collect 
at  the  bottom  of  the  vessel.  This  substance  is  called 
vegetable  albumin. 

Besides  the  albumin,  the  gluten,  and  the  starch, 
other  substances  about  which  this  rough  method  of 
analysis  gives  us  no  information,  are  contained  in  the 
wheat  grain.  For  example,  there  is  woody  matter  or 
cellulose,  and  a  certain  quantity  of  sugar  and  fat. 
It  would  be  possible  to  obtain  a  substance  similar  to 
albumin,  starch,  saccharine  and  fatty  matters,  and 
cellulose,  by  treating  the  stem,  leaves,  and  root  in  a 
similar  fashion,  but  the  cellulose  would  be  in  far 


OBJECTS.]  INTRODUCTORY.  85 

larger  proportion.  Straw,  in  fact,  which  consists  of 
the  dry  stem  and  leaves  of  the  wheat  plant,  is  almost 
wholly  made  up  of  cellulose.  Besides  this,  however, 
it  contains  a  certain  proportion  of  mineral  bodies, 
among  them,  pure  flint  or  silica ;  and,  if  you  should 
ever  see  a  wheat  rick  burnt,  you  will  find  more  or  less 
of  this  silica,  in  a  glassy  condition,  in  the  embers.  In 
the  living  plant,  all  these  bodies  are  combined  with  a 
large  proportion  of  water,  or  are  dissolved,  or  sus- 
pended in  that  fluid.  The  relative  quantity  of  water  is 
much  greater  in  the  stem  and  leaves  than  in  the  seed. 

57.  The  Common  Fowl  and  the  Sub- 
stances of  which  it  is  Composed. 

Everybody  has  seen  a  common  fowl.  It  is  an 
active  creature  which  runs  about  and  sometimes  flies. 
It  has  a  body  covered  with  feathers,  provided  with 
two  wings  and  two  legs,  and  ending  at  one  end  in  a 
neck  terminated  by  a  head  with  a  beak,  between  the 
two  parts  of  which  the  mouth  is  placed.  The  hen 
lays  eggs,  each  of  which  is  inclosed  in  a  hard  shell. 
If  you  break  an  egg  the  contents  flow  out  and  are  seen 
to  consist  of  the  colourless  glairy  "  white  "  and  the 
yellow  "yolk,"  If  the  white  is  collected  by  itself  in 
water  and  then  heated  it  becomes  turbid,  forming  a 
white  solid,  very  similar  to  the  vegetable  albumin, 
which  is  called  animal  albumin. 

If  the  yolk  is  beaten  up  with  water,  no  starch  nor 
cellulose  is  obtained  from  it,  but  there  will  be  plenty 
of  fatty  and  some  saccharine  matter,  besides  substances 
more  or  less  similar  to  albumin  and  gluten. 

The  feathers  of  the  fowl  are  chiefly  composed 
of  horn ;  if  they  are  stripped  off  and  the  body  is 


86  SCIENCE  PRIMERS.  [MATERIAL 

boiled  for  a  long  time,  the  water  will  be  found  to 
contain  a  quantity  of  gelatin,  which  sets  into  a  jelly 
as  it  cools ;  and  the  body  will  fall  to  pieces,  the  bones 
and  the  flesh  separating  from  one  another.  The  bones 
consist  almost  entirely  of  a  substance  which  yields 
gelatin  when  it  is  boiled  in  water,  impregnated  with  a 
large  quantity  of  salts  of  lime,  just  as  the  wood  of  the 
wheat  stem  is  impregnated  with  silica.  The  flesh,  on 
the  other  hand,  will  contain  albumin,  and  some  other 
substances  which  are  very  similar  to  albumin,  termed 
fibrin  and  syntonin. 

In  the  living  bird,  all  these  bodies  are  united  with 
a  great  quantity  of  water,  or  dissolved,  or  suspended 
in  water ;  and  it  must  be  remembered  that  there  are 
sundry  other  constituents  of  the  fowl's  body  and  of  the 
egg,  which  are  left  unmentioned,  as  of  no  present 
importance. 

58.  Certain  Constituents  of  the  Body  are 
very  similar  in  the  Wheat  Plant  and  in  the 
Fowl. 

The  wheat  plant  contains  neither  horn,  nor  gelatin, 
and  the  fowl  contains  neither  starch,  nor  cellulose  ;  but 
the  albumin  of  the  plant  is  very  similar  to  that  of  the 
animal,  and  the  fibrin  and  syntonin  of  the  animal  are 
bodies  closely  allied  to  both  albumin  and  gluten. 

That  there  is  a  close  likeness  between  all  these 
bodies  is  obvious  from  the  fact  that  when  any  of  them 
is  strongly  heated,  or  allowed  to  putrefy,  it  gives  off 
the  same  sort  of  disagreeable  smell;  and  careful 
chemical  analysis  has  shown  that  they  are,  in  fact, 
all  composed  of  the  elements  Carbon,  Hydrogen, 
Oxygen,  and  Nitrogen,  combined  in  very  nearly 


OBJECTS.]  INTRODUCTOR  Y. 


-         87 


the  same  proportions.  Indeed,  charcoal,  which  is 
impure  carbon,  might  be  obtained  by  strongly  heating 
either  a  handful  of  corn,  or  a  piece  of  fowl's  flesh,  in 
a  vessel  from  which  the  air  is  excluded  so  as  to  keep 
the  corn  or  the  flesh  from  burning.  And  if  the  vessel 
were  a  still,  so  that  the  products  of  this  destructive 
distillation,  as  it  is  called,  could  be  condensed  and 
collected,  we  should  find  water  and  ammonia,  in  some 
shape  or  other,  in  the  receiver.  Now  ammonia  is  a 
compound  of  the  elementary  bodies,  nitrogen  and 
hydrogen ;  therefore  (§  50)  both  nitrogen  and  hydro- 
gen must  have  been  contained  in  the  bodies  from 
which  it  is  derived. 

It  is  certain,  then,  that  very  similar  nitrogenous  com- 
pounds form  a  large  part  of  the  bodies  of  both  the 
wheat  plant  and  the  fowl,  and  these  bodies  are  called 
proteids. 

59.  Proteid  Substances  are  met  with  in 
Nature  only  in  Animals  and  Plants;  and 
Animals  and  Plants  always  contain  Pro- 
teids. 

It  is  a  very  remarkable  fact  that  not  only  are  such 
substances  as  albumin,  gluten,  fibrin  and  syntonin, 
known  exclusively  as  products  of  animal  and  vegetable 
bodies  \  but  that  every  animal  and  every  plant,  at  all 
periods  of  its  existence,  contains  one  or  other  of  them, 
though,  in  other  respects,  the  composition  of  living 
bodies  may  vary  indefinitely.  Thus,  some  plants  con- 
tain neither  starch  nor  cellulose,  while  these  substances 
are  found  in  some  animals ;  while  many  animals  contain 
no  horny  matter  and  no  gelatin-yielding  substance. 
So  that  the  matter  which  appears  to  be  the  essential 


88  SCIENCE  PRIMERS.  [MATERIAL 

foundation  of  both  the  animal  and  the  plant  is  the 
proteid  united  with  water;  though  it  is  probable 
that,  in  all  animals  and  plants,  these  are  associated 
with  more  or  less  fatty  and  amyloid  (or  starchy 
and  saccharine)  substances,  and  with  very  small 
quantities  of  certain  mineral  bodies,  of  which  the 
most  important  appear  to  be  phosphorus,  iron, 
lime,  and  potash. 

Thus  there  is  a  substance  composed  of  water 
+  proteids  +  fat  +  amyloids  +  mineral  matters 
which  is  found  in  all  animals  and  plants ;  and,  when 
these  are  alive,  this  substance  is  termed  protoplasm. 

60.  What  is  meant  by  the  word  Living  ? 

The  wheat  plant  in  the  field  is  said  to  be  a  living 
thing;  the  fowl  running  about  the  farmyard  is  also 
said  to  be  a  living  thing.  If  the  plant  is  plucked  up, 
and  if  the  fowl  is  knocked  on  the  head,  they  soon  die 
and  become  dead  things.  Both  the  fowl  and  the 
wheat  plant,  as  we  have  seen,  are  composed  of  the 
same  elements  as  those  which  enter  into  the  com- 
position of  mineral  matter,  though  united  into  com- 
pounds which  do  not  exist  in  the  mineral  world.  Why 
then  do  we  distinguish  this  matter  when  it  takes  the 
shape  of  a  wheat  plant,  or  a  fowl,  as  living  matter  ? 

6 1.  The  Living  Plant  increases  in  Size,  by 
adding  to  the  Substances  which  compose  its 
Body,  like  Substances  ;   these,  however,  are 
not   derived  from   without,   but   are    manu- 
factured within  the  Body  of  the  Plant  from 
simpler  Materials. 

In  the  spring,  a  wheat-field  is  covered  with  small 


OBJECTS.]  INTRO D  UCTOR  Y.  89 

green  plants.  These  grow  taller  and  taller  until  they 
attain  many  times  the  size  which  they  had  when  they 
first  appeared  ;  and  they  produce  the  heads  of  flowers 
which  eventually  change  into  ears  of  corn. 

In  so  far  as  this  is  a  process  of  growth,  accompanied 
by  the  assumption  of  a  definite  form,  it  might  be 
compared  with  the  growth  of  a  crystal  of  salt  in 
brine :  but,  on  closer  examination,  it  turns  out  to  be 
something  very  different.  For  the  crystal  of  salt  grows 
by  taking  to  itself  the  salt  contained  in  the  brine, 
which  is  added  to  its  exterior  ;  whereas  the  plant 
grows  by  addition  to  its  interior :  and  there  is  not  a 
trace  of  the  characteristic  compounds  of  the  plant's 
body,  albumin,  gluten,  starch,  or  cellulose,  or  fat,  in 
the  soil,  or  in  the  water,  or  in  the  air. 

Yet  the  plant  creates  nothing  (§  50)  and,  therefore, 
the  matter  of  the  proteids  and  amyloids  and  fats  which 
it  contains  must  be  supplied  to  it,  and  simply  manu- 
factured, or  combined  in  new  fashions,  in  the  body  of 
the  plant. 

It  is  easy  to  see,  in  a  general  way,  what  the  raw 
materials  are  which  the  plant  works  up,  for  the 
plant  gets  nothing  but  the  materials  supplied  to  it  by 
the  atmosphere  and  by  the  soil.  The  atmosphere 
contains  oxygen  and  nitrogen,  a  little  carbonic  acid 
gas,  a  minute  quantity  of  ammoniacal  salts,  and  a 
variable  proportion  of  water.  The  soil  contains  clay 
and  sand  (silica),  lime,  iron,  potash,  phosphorus, 
sulphur,  ammoniacal  salts,  and  other  matters  which 
are  of  no  importance.  Thus,  between  them,  the  soil 
and  the  atmosphere  contain  all  the  elementary  bodies 
which  we  find  in  the  plant :  but  the  plant  has  to 
separate  them  and  join  them  together  afresh. 


90  SCIENCE  PRIMERS.  [MATERIAL 

Moreover  the  new  matter,  by  the  addition  of  which 
the  plant  grows,  is  not  applied  to  its  outer  surface,  but 
is  manufactured  in  its  interior ;  and  the  new  molecules 
are  diffused  among  the  old  ones. 

62.  The  Living  Plant,  after  it  has  grown 
up,   detaches  part   of   its  Substance,  which 
has  the  Power  of  developing  into  a  similar 
Plant,  as  a  Seed. 

The  grain  of  wheat  is  a  part  of  the  flower  of  the 
wheat  plant,  which,  when  it  becomes  ripe,  is  easily 
separated.  It  contains  a  minute  and  rudimentary 
plant ;  and,  when  it  is  sown,  this  gradually  grows,  or 
becomes  developed  into,  the  perfect  plant,  with  its 
stem,  roots,  leaves  and  flowers,  which  again  give  rise 
to  similar  seeds.  No  mineral  body  runs  through  a 
regular  series  of  changes  of  form  and  size  and  then 
gives  off  parts  of  its  substance  which  take  the  same 
course.  Mineral  bodies  present  no  such  develop- 
ment and  give  off  no  seeds  or  germs.  They  do  not 
reproduce  their  kind. 

63.  The  Living  Animal  increases  in  Size  by 
adding  to  the  Substances  which  compose  its 
Body,  like  Substances  ;   these   however  are 
chiefly  derived  directly  from  other  Animals 
or  from  Plants. 

The  fowl  in  the  farmyard  is  incessantly  pecking 
about  and  swallowing  now  a  grain  of  corn,  and  now 
a  fly  or  a  worm.  In  fact,  it  is  feeding,  and,  as  every 
one  knows,  would  soon  die  if  not  supplied  with  food. 
It  is  also  a  matter  of  every  day  knowledge  that  it 
would  not  be  of  much  use  to  give  a  fowl  the  soil  of 
a  corn-field,  with  plenty  of  air  and  water,  to  eat. 


OBJECTS.]  INTRODUCTORY.  91 

In  this  respect,  the  fowl  is  like  all  other  animals ;  it 
cannot  manufacture  the  proteid  materials  of  its  body, 
but  it  has  to  take  them  ready  made,  or  in  a  con- 
dition which  requires  but  very  slight  modification,  by 
devouring  the  bodies  either  of  other  animals  or  of 
plants.  The  animal  or  vegetable  substances  devoured 
are  taken  into  the  animal's  stomach ;  they  are  there 
digested  or  dissolved ;  and  thus  they  are  fitted  to  be 
distributed  to  all  parts  of  the  fowl's  own  body,  and 
applied  to  its  maintenance  and  growth. 

64.  The  Living  Animal,  after  it  has  grown 
up,  detaches  part  of  its  Substance,  which  has 
the  Power  of  growing  into  a  similar  Animal, 
as  an  Egg. 

The  fowl's  egg  is  formed  in  the  body  of  the  hen, 
and  is,  in  fact,  part  of  her  body  inclosed  in  a  shell 
and  detached.  It  contains  a  minute  rudiment  of  a 
fowl ;  and  when  it  is  kept  at  a  proper  temperature 
by  the  hen's  sitting  upon  it,  or  otherwise,  for  three 
weeks,  this  rudiment  grows,  or  develops,  at  the 
expense  of  the  materials  contained  in  the  yolk  and 
the  white,  into  a  small  bird,  the  chick,  which  is  then 
hatched  and  grows  into  a  fowl.  The  animal,  there- 
fore, is  produced  by  the  development  of  a  germ  in 
the  same  way  as  the  plant ;  and,  in  this  respect,  all 
plants  and  all  animals  agree  with  one  another  and 
differ  from  all  mineral  matter. 

65.  Living    Bodies    differ     from    Mineral 
Bodies   in  their  Essential  Composition,    in 
the  manner  of  their  Growth,  and  in  the  fact 
that  they  are  reproduced  by  Germs. 

Thus   there   is   a  very  broad   distinction  between 


92  SCIENCE  PRIMERS.         [IMMATERIAL 

mineral  matter  and  living  matter.  The  elements  of 
living  matter  are  identical  with  those  of  mineral 
bodies ;  and  the  fundamental  laws  of  matter  and 
motion  apply  as  much  to  living  matter  as  to  mineral 
matter ;  but  every  living  body  is,  as  it  were,  a  com- 
plicated piece  of  mechanism  which  "goes,"  or  lives, 
only  under  certain  conditions.  The  germ  contained 
in  the  fowl's  egg  requires  nothing  but  a  supply  of 
warmth,  within  certain  narrow  limits  of  temperature, 
to  build  the  molecules  of  the  egg  into  the  body  of 
the  chick.  And  the  process  of  development  of  the 
egg,  like  that  of  the  seed,  is  neither  more  nor  less 
mysterious  than  that,  in  virtue  of  which,  the  mole- 
cules of  water,  when  it  is  cooled  down  to  the  freezing- 
point,  build  themselves  up  into  regular  crystals. 

The  further  study  of  living  bodies  leads  to  the 
province  of  Biology,  of  which  there  are  two  great 
divisions  —  Botany,  which  deals  with  plants,  and 
Zoology,  which  treats  of  animals. 

Each  of  these  divisions  has  its  subdivisions — such 
as  Morphology,  which  treats  of  the  form,  structure, 
and  development  of  living  beings,  and  Physiology, 
which  explains  their  actions  or  functions,  besides 
others. 


III.  IMMATERIAL  OBJECTS. 

66.  Mental  Phenomena. 

Material  objects  are  all  either  not  living,  that  is  to 
say,  mineral  bodies,  or  they  are  living  bodies.  Every- 
thing which  occupies  space,  offers  resistance,  has 
weight,  and  transfers  motion,  belongs  to  one  or 


OBJECTS.]  INTROD  UCTOR  Y.  93 

other  of  these  two  great  provinces  of  nature.  The 
sciences  of  Astronomy,  Mineralogy,  Physics,  and 
Chemistry  deal  with  the  former,  while  Biology,  with 
its  two  divisions  of  Zoology  and  Botany,  treats  of 
the  latter.  But  natural  knowledge  is  not  exhausted 
by  this  catalogue  of  its  topics.  In  the  very  first  para- 
graph of  this  Primer,  in  fact,  we  had  occasion  to  [ 
draw  a  distinction  between  Things,  or  material  ob- 
jects, and  Sensations;  and  a  moment's  reflection 
is  sufficient  to  convince  you  that  sensations  are  not 
material  objects.  A  smell  takes  up  no  space  and  has 
no  weight ;  and  to  speak  of  a  pound  or  of  a  cubic 
foot  of  sound,  or  of  brightness,  is,  on  the  face  of  the 
matter,  an  absurdity.  Pleasure  is  said  metaphorically 
to  be  fugitive,  but  you  cannot  imagine  a  pleasure  as 
a  thing  in  motion. 

What  we  call  our  Emotions  are  in  like  manner 
devoid  of  all  the  characters  of  material  bodies.  Love 
and  hatred,  for  example,  cannot  for  a  moment  be  con- 
ceived to  have  shape,  or  weight,  or  momentum.  And 
when,  in  reasoning,  we  think,  our  Thoughts  have 
the  same  lack  of  the  qualities  of  material  things. 

Sensations,  emotions,  and  thoughts,  thus  constitute 
a  peculiar  group  of  natural  phenomena,  which  are 
termed  mental. 

67.  The  order  of  Mental  Phenomena:  Psy- 
chology. 

A  definite  order  obtains  among  mental  phenomena, 
just  as  among  material  phenomena ;  and  there  is  no 
more  chance,  nor  any  accident,  nor  uncaused  event,  in 
the  one  series  than  there  is  in  the  other.  Moreover, 
there  is  a  connection  of  cause  and  effect  between 


Q4  SCIENCE  PRIMERS.  [IMMAT 

L      OBJE 


ERIAL 

CTS. 


certain  material  phenomena  and  certain  mental  phe- 
nomena. Thus,  for  example,  certain  sensations  are 
always  produced  by  the  influence  of  particular  material 
bodies  on  our  organs  of  sense.  The  prick  of  a  pin 
gives  pain,  feathers  feel  soft,  chalk  looks  white,  and  so 
on.  The  study  of  mental  phenomena,  of  the  order 
in  which  they  succeed  one  another,  and  of  the  rela- 
tions of  cause  and  effect  which  obtain  between  them 
and  material  phenomena,  is  the  province  of  the 
science  of  Psychology. 

All  the  phenomena  of  nature  are  either  material 
or  immaterial,  physical  or  mental;  and  there  is  no 
science,  except  such  as  consists  in  the  knowledge 
of  one  or  other  of  these  groups  of  natural  objects, 
and  of  the  relations  which  obtain  between  them. 


THE   END. 


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